Before pumping the company warned me that if this particular septic (made in 1964) didn't have the appropriate bottom that they could not "certify" it and that it would have to get replaced costing over 10K.

I am a Certified Money Lender.

I sent the check, I'll send it certified mail or Ups, my personal favorite, I am in California until July and I still have yet to receive anything from him.

They could do a better job matching same size, age, beds, <6 mo sales in the comp tool but at least it gives a list of area sales too plus last MLS listing's pictures (valuable).As far as pulling lists, yes PS has the most data types (liens, mortgage amount, equity) vs anyone else but its an ugly trueth in the data market place. 

I know we have a company come out once a year to check our fire extinguishers and fire alarms to make sure they are certified up to date.

If you have the right people to help you in the process and that will offer you transparent and honest communication, along with all the pros and cons associated with the marketplace, then it can be great.

I sent them a certified letter for an explanation.

If the initial attempt to reason and create rapport with the neighbor through neighborly conversation is unsuccessful, I'd consider sending a certified letter next so that it's on record, start the clock ticking on that if it does end up being an attorney situation, and make friends with the local code enforcement department officers. 

I also recommend posting a rental listing on Facebook Marketplace. 

When you get S8 certified they explain all this in their class.NEVER let a tenant in early.