I modified the standard invoice the read "Rent Due" and email rental invoices to tenant. 

Can you imagine being the PM who pays a vendor and sends the landlord all the rent while they refuse to pay an invoice?

@Robert AlexisSearch permitsAsk for contract list that performed major work, ideally with scope of work and paid invoices behind it.Search liens and lien releases While there are a lot of flippers that do fine work without pulling permits, it would give me pause if they didn't.  

I attached the photo of 2 invoices they sent me and my wife paid them already

After inspection, the invoice came at $560, same vendor. 

Be sure you understand the full process if you sign up for one of the utils "convenient" options.As a PM, daily I review, approve, and initial every invoice that comes through the front door, every month, before passing them to accounting for payment from the Owners funds.

Enter a maintenance request, assign a vendor, attach a fake invoice.

So if I invoice my friend for the work and he can write that off to prove less profit, combined will we pay less taxes?

It lets you attach all of your receipts and invoices and spits them out at the end of the year as a zip file to go along with your tax report.

If they charge, keep the invoice and take it from security deposit.