I just had a look at the eBay listing and I think that you are pretty safe.
Firstly, the seller only wants cash (no PayPal etc.) and requests settlement within 7 days of the end of the auction. That is plenty of time to check out the boat, the 'owner's' entitlement to sell and to satisfy yourself about the condition.
If it turns out to be a load of old nails and not as described (let's ignore the possibility of fraud), then don't go ahead. You can't even get a negative feedback from the vendor now that eBay has changed its rules.
I suppose that there is a slight possibility that you might be pursued for breach of contract but this is a tough one for the vendor to carry if the boat really isn't as descibed.
Anyhow, she is a clean looking craft and you might nab a real bargain. I would want to check the age of the canvas though.