I depends on how good a deal we're talking about. For example, if someone posted a copy of Project Justice on the Dreamcast for $50 instead of its usual $70+ I'd probably ask some questions first, however if it were under $30 I'd probably hit the BIN. Either way, as a buyer you are protected by Ebay's buyer protection so if you end up getting an item that is poorly or inaccurately described, Ebay will force the refund regardless of the seller's stated policies.
I have quite a bit of experience as a seller and buyer on Ebay, and Ebay is overwhelmingly more sympathetic towards the buyer, and will side with them 95% of the time, even in some situations where the seller is probably in the right. As a seller it can be very frustrating, but as a buyer it gives you security in taking chances with sellers that don't accurately/thoroughly describe their item(s). In a few cases I have received items that were inaccurate or deceptive in their description (pictured one thing, got another), and Ebay has sided with me in every instance, forcing a refund. It can be a process if this happens (having to open up a case and wait for Ebay to intervene), but if you're willing to wait a few days, Ebay will most likely side with you and give you your money back.
Just one more thing, NEVER EVER use the same account for selling and buying if you do this. I have had two situations where I opened up a case against a seller for inaccurately describing an item, the seller got pissed after being forced to issue a refund, and decided to take revenge by buyer some of my items (with no intention of paying for them) just so they could leave me negative feedback. Doing this often resulted in that user getting banned, but because they pisses them off even more, they came back with dummy accounts and continues to harass me. Ebay does not ban IP addresses, so the best you can do is block their individual accounts, but not until they've already falsely bought some of your items and left fake negative feedback. However if you keep your accounts separate for buying and selling, you have nothing to worry about.