They seem to be legitamite.
https://forums.macrumors.com/threads/615279/
However, though you said you would prefer to steer clear of eBay. I have bought a few computers, many computer components, numerous other electronics and other miscellaneous stuff. I have not had a bad experience as a Buyer but one as a seller.
I just make sure the seller has a good feedback rating as a seller and have never had a problem, everything has arrived as described and the item is not out of norm nor the account is suddenly selling high ticket items again after an extended lull. For smaller sellers I look at their few reviews, ad layout, price, and how well they communicate to decide whether they are worth the gamble.
Since I only buy from those whom accept Paypal if there is a problem I could apply for a refund. At the same time you can tell your credit card company or bank to reverse the charges and force Paypals hand
😛.
I think it is the sellers whom have it tougher since they can not pick and choose who bids or hits buy it now.
When all is said and done I think your odds of getting a lemon are the same with an online used Mac store as they are with an eBay seller. If you use some discretion when buying.