We have not had an issue with multiple listings on different Airbnb accounts before. 

Quote from @Albert Johnson: Tenants never complained of a health issue.

If you're refinancing six properties, bundling them into a portfolio loan might help you consolidate debt, reduce rates, and avoid individual property issues like this.Negotiate Closing Costs or LTV with Kiavi.

Plumbing company says its the only way to resolve the issue I have.

The seller is not very tech savvy and is going through some life issues so he isn't being very helpful in this.

What type of interview do you do with existing tenant(s) to ask them about maintenance issues?

@William Causey depends on the transaction and the parties involved.Agree with @Dennis McNeely on some of the transaction costs.A different issue though is with an Assignment, the buyer gets to see what you paid for the property.

There is also parking per unit and impervious cover that could be an issue.

You need to find out the source of the issue first before you start charging the tenant. 

That's the reason there are so many fourplexes and so few fiveplexes or even sixplexes.From what I gather, post offices and utility companies rarely care much about the permitting/zoning issues, so it probably wouldn't have been hard to get those set up.