1) If there was no agreement beforehand to pay--and that includes no implied or implicit agreement--then you should probably not have to pay. For example, if there is a sign on the shop wall about the cost of renting equipment, or the proprietor mentioned that "you could use the equipment as long as you cover the cost," or something like that, that *may* be enough to find an agreement that you'd pay rental. But without either an explicit or implicit agreement, you would probably not be liable.2) You may therefore have a good defense. Whether you should defend or else "pay it and move on" depends on how you value your time; whether you'd undertake the defense yourself or hire an attorney (if you hire a lawyer, you'd likely pas as much or more defending as paying); how much fighting will stress you; what your financial resources are. Another option is to try to settle for a lesser amount.