Don't think it's just quite that black and white BSA_54A10
Fair number of our better suppliers sell on Ebay, some are quite easy to spot by the stock and address, most don't sell under their known trade name.
your correct that there is some crap on there, most of us will have been caught out at some point, but there is also some good stuff also some over priced good stuff in as much as if you know the price a trader is charging for bits you can spot the same bits on Ebay with the price hyped up by the inclusion of RGS in the description and people who don't know better will pay up.
It is an auction after all, unless you know what your after and what it is worth - don't bid
If you do bid - know and stick to your valuation, don't bid over
Look to see who is bidding, Ebay will mark with a question mark anybody who has a history of bidding with the seller, ( some sellers help each other out by bidding for each other, sometimes they have more than one identity (recent court case)).
Also if you indicate an interest ( question to seller ) and there is little interest you might find a bid all of a sudden toward the end to umph the price up - don't bid
Nothing your going to buy on Ebay is likely to be life threatening if you don't win it - if it's suspect in quality or price , don't bid