What questions should be asked? What would you expect the dealer to do or have done before you take possession? Does a dealer ever have a warranty (30-60-90 days??) for an older boat??
JB in WTexas

I think it would he highly unusual for a dealer to offer a warranty on a pre-owned boat, but you never know. Most are going to be sold as-is and it's up to you to do the inspection and arrange for a compression check, or have a knowledgeable friend go with you.

Bob is spot on, if youre not too boat savvy, bring someone who is. Go run the boat, not a trip around the marina and back, but go burn half a tank and run it HARD. Im not saying try and break it, but expose any weaknesses. flip every switch, push every button, jiggle every wire you see, then repeat.

take a GOOD look at the flippin trailer!! A broken axle or fried bearing before your first trip out will pi$$ you off like you wouldn't believe possible,
So what kinda boat are you looking at getting anyhow?

The dealer bought that boat, they have already done a compression test etc. If they haven't I would consider looking elsewhere.

Ask if they go over trade ins before selling. Ask if compression check done and what it is, how many hours on engine, if everything works, do batteries need replaced, etc. If they cannot or will not give answers then go elsewhere. The dealers that will give answers are the ones that understand 1 unsatisfied customer can ruin their business.