I'm under contract to buy a house. Sewer scope failed because of 2 significant pooling spots. Camera was completely submerged. Plumber recommends regrading the line but the house slopes down from the street so I think gravity might be a problem in general, particularly since the line was completely replaced 5 years ago. This doesn't seem like a simple replacement of a sewer line and I'm trying to figure out whether I should walk away from the deal. What other options are available if regrading the line doesn't resolve the issue?

If proper pitch is an issue a whole house pump must be installed
Re grading will probably not work
Since the entire line was replaced 5 years ago it was never properly installed or backfilled
Your looking at quite an expensive project to replace the entire sewer again and possibly adding a sewage pump to the city sewer if getting the proper pitch is an issue

so why did you suspect there was something wrong in the first place?

sewer was replaced 5 years ago, the average buyer would just assume it was done correctly and pass inspection.

I got the inspection out of an abundance of caution and glad I did. Seems like a costly repair.

run

run fast

run far

run yesterday

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

if you really like the house then you'll have to do some negotiating with the owner/s.
it seems to me that if the house survived all these years with the sewer pipe they had that perhaps the new installation was faulty and can be corrected.
the house can't be sold with a known defect as serious as it has... at least not for the price you arrived at.
someone has to do some serious research into this problem.
it could be as simple as exposing the problem areas and packing sand under the bellies.
OR it could be that there is not enough height to have the sewage flow by gravity so a whole house pumping system would need to be installed.
so if you want it, go for it.

I would research the heck out of the five year old job.

Who was the contractor? what was the scope of work, the extent of the repair, from where to where? From under the house to the property line? Or from where it exists the house downstream? Is there a basement where the main drain is or under slab? Was that job permitted and inspected? Where are the trouble spots? Under the house or outside where they can be excavated much easier?

Also bear in mind sometimes a cam inspection can be deceiving. Water ponding at the bottom of the pipe can be due to a low spot aka belly, but could also be due to a partial blockage downstream acting as a dam. For this reason it's best to have the line snaked or jetted prior to camera inspection. Also be mindful that a camera is smallish, may be 1.5" in diameter with its casing if that, if the water is 1" deep in a 4" pipe, it will look fully submerged but the pipe is far from being full of water.

I learned from the seller that the sewer replacement 5 years ago was done by a construction company, not a certified sewer contractor. Any thoughts about why someone wouldn't use an expert??

just because someone owns a sewer replacement company doesn't mean they are an "expert".
sewer pipe and fittings are sold at most home centers or lumber yards.
while the installation of the pipe might be faulty, the bedding the pipe sits on as well as the fill place on top of could also be to blame.
at this point, no body knows.

I think you need to take a step back and consider the whole situation here....two bellies in the line don't mean that the whole line has negative slope. The house may be downhill from the road, but without knowing how deep the main sewer is, you don't know if the slope of the house line is correct.

Also, as Sum pointed out, just because the camera went underwater in the bellies doesn't mean the line was completely filled with water. If the line was completely full of water, indicating a possible negative slope, surely there would be performance problems like slow drains, gurgling flushes, etc.

The line may not have been installed with a perfectly consistent slope, as indicated by the bellies, but that doesn't mean it's completely unserviceable. After all it's been working fine for 5 years. This is just me, but I would rather have a 5-yr old PVC line with a couple of low spots than a 75-yr old cast iron line that is nearing the end of its serviceable life.