Ok, so now we know what lane you're in.
Maybe you don't belong here. This is a thread about buying a boat, not about how to be a shitbag flipper and get one over on your customers.
I know you probably don't realize this but professional flippers give off a pretty obvious vibe when you encounter them as a seller. It really should be no surprise that sellers don't want to give you any sort of leeway.
Sometimes you gotta all but fix shit to meet the agreed upon conditions of the sale. "I tell ya what, I'll fix the trans leak it and if it goes through the gears without issues I pay X" type shit. And if you don't come off like a scumbag most non scumbags will stick to their end of it.
Sellers aren't stupid. Trying to be guarded with information is the kind of shit that clues them into the fact that you're a flipper and likely to be trying to pull a fast one on them.
I have less than zero sympathy for when you high volume types who make a business out of this shit and run every transaction as though it's adversarial (because it is) get fucked. In fact I wish y'all got fucked more often. You serve no useful economic purpose. You're basically a liquidity provider. You are only useful in a small minority of transactions you take part in and you are a needless middle man jacking up cost in the vast majority of them.
Edit: It's worth noting that there's a couple people here who more or less have businesses flipping shit but don't have the aura of scummy flipper about them because they're upmarket enough that being scummy for a buck here and there just doesn't make sense.
I've fixed shit in people's yards before. One of my favorite shitboxes I showed up in an identical shitbox with the radiator the new one needed in hand. I let the other guy know this was my plan. If the other guy says there's only one (realistically fixable) problem and he won't let you fix it that should be a red flag.
My front end loader we rigged up a battery and bypassed the fiery but mostly peaceful wiring harness to see if it'd crank. It didn't so we bore scoped it. Looked a tad questionable so the guy threw in some forks on the condition that I spend an hour helping him move some shit as he was cleaning out the property. I still bought it and it eventually ran so it all turned out good in the end.