Staining an oil finish

I'm considering buying a mahogany g****r body on ebay. The guitar shipped from the factory with an oil finish, and the seller tells me that the previous owner stained it to a darker color. This raises a number of questions for me.

What would be the proper way to do a refinish like this? I'm assuming one would need to remove the factory finish somehow, stain it, then re-oil it. Is it possible that the owner stained it without removing the oil finish? If so, would that prevent the stain from penetrating the wood, and allow me to remove it? Also, if the owner stained over the factory finish, then did not apply another layer of finish, should I re-oil it? Could I use any oil, or do I need to be concerned about incompatibilities between the factory oil and the one I choose (I think I'd use tru oil if I had my choice).

 

Fair enough, Hambone, but one of the reasons I posted here was that you, in particular, usually have lots to say about this type of stuff. What if we just pretend it's a bass body?