Purchase advice

Which islands do you have in mind? If the Bahamas, then pretty much anything can get you there safely, even a carver. If you mean the Caribbean, it s a lot rougher with longer open passages requiring a more seaworthy vessel.

Initial build quality, maintenance and upgrades are far more important than fresh water vs salt

Welcome to YF. What Pascal says is sage advice. However, in looking at 20 year old boats, what is your ability to assess, repair, maintain, etc. Is this is a beginner boat for you?

When you have a candidate boat in mind, you can ask around for surveyor -- marine and mechanical -- recommendations in the area. And you'll also want the recommended mechanical surveyor to be a specialist on whatever engines are in the boat, once known after you identify the target.

Surveyor recommendations based on past performance can often help you sort the wheat from the chaff.

Boat value is largely dependent on previous care, or lack thereof. You can usually also ask (in your offer) to review previous maintenance records early in the (potential) purchase process. "None" would be a hint. Decent records, especially engine and genset and including things like lube oil analysis results, could be a positive.

-Chris

Ditto to what Chris said above:
Hire a "hull surveyor" for the hull and all systems and a separate "mechanical surveyor" for the engines and generator. You can usually find reputable surveyors by asking right here on YF.

And whatever you do, do not rely on a seller provided survey or any surveyor recommended by seller or broker!

I agree with Pascal's post # 9, but I have to add an *

*Broker's Buyer. If you engage an appropriate broker to work solely on your behalf as buyer, that broker should be someone you trust and who is capable of making an appropriate recommendation.

But do not rely on a seller provided survey nor on a listing broker's recommendation!

The reason I didn’t mention a buyers broker recommendation for a surveyor is that while a buyers broker works for the buyer, it is also in his interest for the deal to close so some may avoid recommending a “picky surveyor”

The key word is "trustworthy."