I have found two offshore crew spots here, one 1000nm from USVI to Bermuda, and the other a 3000nm Atlantic crossing. I did whatever homework I could on both before signing on. In one case I flew 800miles to meet the skipper and inspect the boat, and he had a chance to check me out as well. You are are putting your safety and sanity on the line
with respect to both boat and skipper, so it is about doing your best minimizing risk and maximizing your comfort level.
In the end, I would not have traded either experience, but there are lots of horror stories too. Oh, and one crew member on the longer trip was sick for 17 days...so the surprises can go both ways.