I made up my own sites, each specifically for a set market. Never done it before so it's perfectly feasible for anyone if I can do it.
enduropics quality equestrian photography and
Dod's Pics - Motocross Photography
Both have been promoted in the relevant online communities and now bring in a fair amount of sales. Dodspics is getting roughly 20000 hits a month in the middle of the season so it's not bad. It's linked on all the main sites though so it gets decent publicity even though I still haven't got metatags etc sorted out. It's just about to be revamped for something a bit more stylish.
The most difficult thing was the integration of the shopping cart initially through paypal.