I switched tire dealers a few years ago. I bought a set of 13.6*38's for my M, from my old dealer, had him come out and install them. Less than a month later I found one of them flat. Nothing in the tire, and no sign of a puncture in the casing, just a pinhole in the tube. The dealer said it was a defective tube, and there was NO WARRANTY ON TUBES. If the tractor had been at home, after I got the run around from the dealer, I would have fixed it myself, but it was way across town at another farm. I had to eat the whole thing, road call, pump service, AND, a new tube (at cost, WHOOPEE!!). He lost all my tire business right there.
When the valve stem on the other side rotted off the next summer, I bought a tube from a different dealer, and fixed it myself. After that I swore "no more tire service calls, as long as I can stand up beside the tractor and do it myself".