people bought used cooler, they never saw it operate. called us, we told them it had a clogged cap tube. we told them 3 possible scenarios. we got their permission to try the 1st ,least expensive option. it worked for 5 hrs. we called on follow up that evening, they said it was down to temp. they called back approx, 1 half hour later, and said it quit. they did not pay us. was told they sent check out in mail, that same afternoon, after we left. we agreed to order the parts they needed, to go on, with level 2, repair. they said ok. after 5 business days, no check , they began pressuring us to continue repair regardless, or they will sue us and make us replace the used cooler with a new one. we have done nothing wrong. what should we do?