A bit OT but:
I'd rather say that _ebay_ and amazon are VERY dangerous cause a lot of sellers don't know what they are selling!
discogs has its own pitfalls, but in general the sellers there know what they are selling because it is a specialised platform and take greater care than on other sites. What has happened to me on discogs once as a buyer and once as a seller was that, because it is community generated content, the listed item had changed between putting it online and the actual sale. So, for example I can add a standard UK-issue CD and someone else can come along who doesn't yet understand how discogs works and change it to the limited US-issue. Now someone clicks 'buy' and sadness ensues. With a large collection and lots of items for sale it is nearly impossible to track every stupid change. So, if you really care about some minor detail and getting the exact issue I'd advise you to contact the seller first. This has worked really well for me, however.