It's nice watching someone else's dog because you don't have to worry about training the bad habits out of them. You get to be like the uncle who gives their nephew nothing by candy and violent video games. The dog I was watching the other week would pull like crazy whenever you'd take him for walks. By all accounts a bad habit. It didn't bother me much since he was pretty small, but I was mindful that I shouldn't encourage his behavior. I made the mistake of clipping his leash to a key ring on his collar instead of the D-ring on his collar, and once while he was pulling he broke the key ring and took off after a squirrel. I imagine that in his mind all that pulling is now worth it since he finally broke free. I'd probably be upset if it was my dog.