Recent purchase: drain backing up

[Ed S.]

I've had a drain back up and flood a room twice since moving in. There was nothing disclosed about this issue. After removing wall around drain I found mold which I then tore out all the sheetrock until there was no more. After the second snaking of the drain I had the drain guys run a camera and they diagnosed the problem to be a poorly pitched pipe which is causing waste to build up etc. 

Sounds like the drain guy has been out before for this issue and said it looks like the pipe was replaced but done incorrectly or incompletely. So far this expense has added up and has more to go. 

My question to BP is, are the sellers liable for this issue? I don't have pictures of mold but I do have the situation at hand including receipts and gutted walls. Thanks for any help or advice on this!