Buyer asking for repairs

[Clayton Gabert]

I sold a house to a buyer 2 weeks ago. Part of the agreement was I had to fix a broken sewer line that  was found during inspection. The buyers father owns a plumbing company and I used someone they know to scope the line and fix the line and we went forward and had settlement. Now two weeks after settlement the sink backed up and the same guy scoped line and says there may be a problem with in about eight feet of the house and they're asking me to fix it. Bad thing it's under a concrete patio. Crazy thing is the plumbing guy scoped the line at least five times and never found this issue the first time. Responsible or not?