with caution
When I was boat shopping last year (small CB trailerable boats) I did bid on one via eBay motors. I didn't get it as the price got too rich for my blood. Here are a few points that I think you should consider.
1. the boat either needs to be near you or you need to have someone you trust who is near it to inspect it before you bid. In my case the boat was just down the road from my father, an experienced sailor.
2. If the boat is a good deal, the snipers will probably come out at the last minute. I watched the boat I bid on rise in price > 50% in the last 10 minutes of the auction as numerous sniping engines stepped in with bids. I suggest learning about sniping before you bid on a boat.
So, inspect it, know what it is worth, and bid accordingly. Of course, there is a big difference between using eBay to buy an 18' CB dinghy vs. a 45' keel boat. The money I bid was within my risk tolerance.