[Advice from experienced avatar modders]

I'm fairly proficiant at modding my own avatars but I was looking for advice on providing my modding services to others, mainly textures.

Is there a way to edit the textures of your clients objects/avatars or do you have to purchase the item yourself and would you include that cost into your services or is keeping up with popular items just a cost of doing business?

I'd appreciate any advice for pricing or other pitfalls  as well!