Buyer requesting plumbing repair after closing, already paid 15k.

[Tony Medler]

Hi Everyone, I finished my first flip and I'm running into issues after the closing.  I paid a plumber to fix some bellies in the sewage line, but it looks like all of the issues weren't fixed.  One of the bathrooms keeps backing up and the plumber isn't living up to his 1 year warranty.  

He's trying to say the issue was caused by something I did after he finished his work and refuses to go back to the property and fix the issue, which of course it wasn't.  There's no evidence to suggest the issues are caused by anything other than his inability to do the work correctly.

Now the new owner is coming back to me and requesting I pay for any further repairs.  

My realtor has advised me to contact the plumber and push him to go back out and fix the issue based on what I've paid him for already, and has advised me to write/email him so everything can be documented.  

Has anyone run into a similar situation?  If so, any advice would be appreciated.