With the small amount of tracking I've done, I'd say it depends on the dog and the bond you have w/the dog. Both mine tracked me extremely well and eagerly their first time out. After just a few, I tracked someone else w/ Caleb, and he did very well. I think it helped that we were tracking a handler/dog team, as he was probably more interested in finding the dog than the guy. Caleb genuinely seems to enjoy it, and is very easy to get to track. He's good, too. It shouldn't take much for a dog who enjoys it to switch to a stranger, as long as he understands that's what you want. Using yourself is just easiest, because (hopefully) they're going to have a natural inclination to seek you out.