Here are some tips for avoiding over-used content...

When shopping for content, sort by date. If it's over 2 years old, buy it, but use it as filler content. Don't build sites/galleries prominently featuring that model.

Surf AVS's occasionally. For example, if you have a "bear" photoset, search for "bear" sites on an AVS. If you see that particular set featured MANY times... avoid it like the plague.

Don't buy ultra-cheap content... if you do, use it as filler content only. The chances are... it's cheap for a reason.