Why are AB Yachts so cheap on the used boat market ?

low quality = low price.

I see two 78's for sale in Italy. One is a 2008 for $2.2 million and the other a 2006 for $958,000. It's only the 2006 that's exceptionally cheap but notice that the description says it needs some painting on the right side. That brings about many questions on that particular boat.

One other reason is that the market for Jet's in that size range is limited.

You can't determine whether a price is low or not without seeing the boat. I know the one 2006 has some issues. That's the one for 860k Euro's or $958k. The 2001 for $434k is quite consistent with other comparable boats. Leopards for $423k and $412k, Azimut for $417k. These are all 75' 2001 low end express type boats. They aren't going to price with someone like Sunseeker and definitely not close to someone like Hatteras.

I think we answered with the reasons above, but I'll add one and that is location of the boats.

Which also builds low quality yachts.

Interesting that I was discussing this with an AB yachts dealer from Rome a coupe weeks ago, and the reason is the Jet drives and the market demand for this sub 80/90 feet is limited. Jet drives cost a fortune to install, and you need the hull for them.
An AB Yachts 58 had a listing price from 1.8 million EUROS in 2008.

On the handling side and workmanship I would consider AB Yachts a better product to a Pershing and Mangusta, and the engineer who did the hulls and founded the company Arnabodi was/is an expert in the area of the propulsion and hulls, in a military commercial level before he started up the company.
I think the main reason of the lower used prices is that the design of the smaller AB Yachts (especially the 78) is not as much admired as that of the Pershing or Mangusta. Lets be honest Fulvio de Simoni, and Stefano Righini did a spectacular long term design project respectively on the two brands I mention above. That means that when you go in Saint Tropez with a Mangusta or a Pershing, each and everyone will recognize these boats.

Size wise AB Yachts also offer less space then the competition, and some areas are a bit a catch like less wide side decks on both the AB Yachts 68 and 78, which was improved in later models. Also for example the most friendly AB 78 layout is the 3 cabin layout, fourth cabin version had a twin bunk berth to port side which is also a bit of let down for a 24 meter.
That they have less space is not a bad thing, that means that AB is a boat build from the hull up, then the cabin down. That is what Arnaboldi said back in the days at Genoa, and I guess you gotta believe him. BTW I am not saying that a Pershing or a Mangusta is build cabin first, but I am sure there is some compromise in the design.
Be also sure that you are looking for a real 78, as some brokers advertise the 72 Follia, 75 (72 with big bathing platform) as a 78. The real 78 is the one with the coach roof (HT) similar to that of 90. That cheap 78 around on YW seems to be a non completed never collected boat.

Some years ago I was in Genoa boat show, and the only builders which would offer a test drive in rough seas where; Guy Couach, Italcraft, and AB Yachts (at the time AB Yachts was still not owned by FIPA).

Fipa Maiora apart being expensive and fully custom is one of the few builders who AFAIK can built if you want a fully classed cross of Malta 20 meter or upwards. I guess you have to build low quality for that to be possible. Also up until the recession hit Italy the hardest (2011 till 2014) the 20 and 24 meters models where some of the boats who kept a very high price in the used market value here in the med. Not that this has always to do with quality to be fair.

BTW other boats worth looking if high performance and sea keeping qualities are on the top list would be an Italcraft 70 Drago, and the Alfamarine 78.

And: OTAM 80 (Hull designed by Fabio Buzzi), Baia 70 Italia, Baia 80 Atlantica, Sunseeker Predators

I hope you are not serious in this quote as Sunseekers are always the cheaper of the price bracket, and quality is just above average in my book and it is a full blown production boat.
2007/8s Predators are selling for minus 3/4s of a million Euros, atm. Even Azimut S sell more to this.
I guess put a lot of shiny adverts everywhere and people start to believe it

Give me an AB Yacht over a Sunseeker any-day.

Sunseeker Predators are very over rated boats in my book, very nice in the harbours never to impressive in bad weather.
Baia is among the best if you want surface drive boats, even better to a Pershing.
Otam is more a direct competitor to a Magnum, and I guess that is another level all alone.

Agreed. In reality it is a less spectacular more conservative sport yacht design. Think of an AB Yachts as a woman with a some soft make up, unlike others which are full of it.

I wouldn't say that. I've run several Sunseekers. They all have rode great. I ran a new 73' Manhattan a year ago into 5-6' head seas and cruised right along at 26 knots, there wasn't an ounce of water over the rubrail in a 50NM run. I run an '07 62' Predator and it too is a great riding boat. Better than any other 60-65' express or MY. Baia build quality is very average. A friend of mine used to run an 80'.

The 62 Predator is an okay hull. Have to disagree on the 73, good boat in following seas, just cuts it in head seas.
You do not get wet in many of the Sunseekers that is true, but the slamming is a lot especially when waves start to become deeper.

Depends on the age of the Baia, I was speaking about the combination of hull and surface drives.
The yard was just a 5/10 in the installation (electrics) department prior to 2000, and improved after 2003/4.
The 63 Azzurra would be one of the best hulls in that size for surface drives, and rough water handling, it even competes with a Magnum of similar size.

Ok.....Pershing is definitely not a boat well made, and if you try to navigate in rough sea you will destroy the boat. The quality of Baia is simply crap, but the hull is good.
The Otam 80 has some issues, but not because Buzzi. He designed a spectacular boat, but then Otam added a lot of not necessary weights, and the boat does not perform that well.
Mangusta....not a bad boat, not a bad hull, better made than the other I mentioned, but make sure you have a stabilizer onboard, other wise when at anchor you will be deeply sea sick, the boat rolls like crazy.
AB has a great hull, and a quality superior than Azimut, Pershing, Sunseeker, Azimut and Baia.
Now...let's go to the point : if you want a boat that has the space of a villa inside, well that boat will never be good on sea except the sea is flat. And if you want a boat that performs well on rough sea, then the space inside will be much less than a boat that looks like a summer villa. Why? For rough sea you need a deep V (best will be 24° deadrise from bow to stern, minimum will be 22°), and the bow must be thin, otherwise you will slam on waves. So the boats that go well in rough sea are slimmer, which means less space inside.
Last comment : the design works when it is studied for the performances. A boat is an object that navigate, having a cool design that makes a boat not able to navigate in rough water is simply stupid....but humans are in general not very smart, and this is why Azimut, Ferretti, Sealine, Bavaria, Beneteau and many others keep selling yachts.