I neglected to mention I had been using QBO to send invoices and collect ACH payments (just in the last six months or so) but I don't like that all of the payments go to one bank account. 

At the end of the year I got the yearly invoice which included the transaction fee for the incomplete transfer.

I paid my invoice & that was the end of it... until now.

So basically that company sends the park manager a bill of the itemized charges of w, s, e for each home and then the manager will just manually send over an invoice to each tenant showing & billing them their individual utility charges?

If you have an invoice from a 3rd party licensed HVAC saying the unit is working just fine, then that's that.

An investor friend of mine uses Quickbooks which he sends an invoice to the tenant and they have the option to either pay via check or click on credit card payment.

Once the work is completed, submit the Invoices and they'll release the other $7.500 (or whatever is approved) to you. 

Do they mark up the invoice if something happens such as a rehab?

Long story short, we sent him a disposition of deposit with an invoice because his deposit didn't cover all repairs.

But the easier ones tend to be more expensive, and I don't mind paperwork (for now) to get better terms, so I'm stuck with draw inspections, lien waivers, invoices/receipts, etc.