What should I do if I think someone is stealing tutorials? I'm not quite sure, but I saw two tutorials that were exactly the same, the same wording, the same pictures...is there something I should do?

I would wait and see if they are EXACTLY the same. if so, talk to the person and see if it is just a conicidence. If not, ask them politely to remove it. I really am not an expert at this ;)

how do you know he stole it? could it just be some business arrangement or they gave him permission to use it.

I don't KNOW he stole it. The thing is they're exactly the same...

I would check the entire site for any indication of permission to use the tutorials- I once found a tutorial that was exactly the same as another I saw, and after some poking around I found on one of the pages that the original author allowed the other person to use them.