Im definitely agreeing with Shadowknight1 here, the guy reselling sounds very dodgy, and is more than likely taking advantage of people on ebay, and its potentially less about the possibility that shapeways shop version is under-priced.
Therfore competing with this guy does two things,
1 - it means you have to (to some degree) think about taking advantage of people as well, by charging several times more for something which was in fact much cheaper to print. I wouldnt rule it out however that the original models being sold on shapeways could be underpriced. But still... Unless you advertise them as unique and rare objects to deceive people, your already not able to compete with this guy.
2 - Doesnt solve the fact that this guy is making money (and will continue to make money) off a product you spent time and worked on making available to sell to people.
Id be doing everything possible to get rid of this guy.
Ive had a case like this in the past (not related to shapeways) where someone credited themselves with work Id done, then started selling said work. I sent a warning email as soon as someone informed me of it, and was a matter of hours away from talking to my legal contacts about options, when the guy backed down and did as I asked.
I feel as if I got it easy though, this ebay seller could be more of a challenge.