Man that is your dog, try to understand that guy, if he's a nice guy he will give you the dog back...you also offered him money! if he's not reasonable to understand that, take that dog with pure force...if the guy is a gangstar and you don't want to get in that shit let him go and watch out...Would be interesting to know if he bought the dog from someone else...
My personal choice...the thing should be solved at place when you've seen the tattoo...