A couple of years ago I'd maybe have to do an 'item not received' dispute once or twice a year at the most (I buy a lot on Ebay), but lately more and more sellers just seem to either not bother sending the item at all.
In the last two months I've bought 12 items on Ebay and have had to start Item Not Received disputes for four of them, as nothing was received and there was no reply when I politely tried to contact the sellers. This has happened a lot over the past year or so.
I check feedback before buying/bidding and it's usually sellers with 100% or 99.something feedback that do this.