Or, and with all due respect, a wholesaler…I second @Tom S. opinion/comment that you should pass on this one.plenty of fish in the sea and this one's a poisonous snake.

One of them touches the ear and thinks it's a fan, one of them touches the trunk and thinks it's a snake, one of them touches a leg and thinks it’s a tree trunk and so on.

Odd are you are out of luck and would spend more time and $ trying to win a lawsuit, then snaking the pipe and installing a new sump pump. 

Ron the sewer rat or Johns sewer and drain are two that I hire routinely to consult or actually do sewer scopes, snakes, or repairs.

A lot of snakes in the industry who will just tell the seller (if you weren't honest with them) or the agent.

We had a plumber come out and clean the lines with a snake and thought the issue was fixed.

We try pretty hard to keep the snakes at bay.

Think of a snake trying to eat a pig.

We require painting skills(trim and wall paint without making a mess, operate a paint sprayer and power washer, drywall hang and patch, click lock flooring installation, basic plumbing: install faucet, tub-shower, shut-off valves, install repair kitchen and bath drains, snake a drain.

Otherwise, I would call a rooter company to snake the line.