Yes, it will be on abe and in catalogs soon, I suspect. It was not Ross or Nick who bought this. I can imagine that it must be a bookseller. It could be a private buyer, but really high end booksellers do not buy on ebay, preferring to pay twice the ebay price through dealers. I tried to sell a book (the Big White Book) a couple years ago for $750. I could not do it. Then a couple weeks later a high end bookseller put it in his catalog and sold it for $1500. His copy was identical to mine.
A lot of it is crap. But he could make a good painting. I don't think he put a lot of effort into the paintings for the books. But then I have seen some that were very good. Raw, emotional stuff. Screaming faces, tortured little stick-man bodies...they stand out when you see them.
Or it could be a bookseller with more than one account, if that's possible to have on ebay, or he could have used a friend's or girlfriend's account. It'll be interesting to see if it now pops up on Abebooks.
the only reason, I can see, if you couldn't sell this beauty for 750. was, that no serious collector got aware of your sale. I think it definitely IS worth the 1500. it went for later. With more to come when the economy raises again. In a way, they are one-of-a-kind-items: different photographs on the cover-titles.
you'd be surprised how many collectors would buy a book from, say, ken sanders for $1500 even when a search on abe turns up the same book for $1000. the "prestigious" booksellers get a premium from collectors who want advice on what to buy next and just want to own it, rather than search for it (so they pay a bookseller to search for it for them and offer whatever price). i think, of course, that this is insane, but it happens pretty often.