Per other listings for Trek Madones of various vintgages on eBay, it seems competitively priced, but it will only prove to be a good deal if (a) it fits you and (b) it's in the condition the seller indicates. I say "seems" because an advertised price may have little to do with what price something ultimately sells for. Is this a local sale? Can you meet the seller at a bike shop for a test ride and to pay a mechanic to examine it or examine it yourself?

ETA: Sorry; I didn't see your post that you've already ridden it and that it fits. Nevermind. If you like the bike and it's in good condition, then go for it!