But things like this concerns me, sometimes they just forward invoices and they do not tackle the problems for what they were hired, I think. 

Hey Adam,While it's prudent to have the same inspector go back on your first few deals, it will make sense at some point to just collect the invoices from the contractor that completed the work, ensure they're licensed for the work that requires licenses, and sufficient pictures. 

Secondly, you have no evidence it was done by a professional and don't even have an invoice.

Although he has a business name "Absolute Carpentry" on his invoices , he requested checks for payment be made out to his own name , not the business name , which we did. 

You should have all of the invoices he gave you for payment.

Collect all invoices for the phase at end of the phaseMy higher level opinion is to hire people for their trades, and take those out of the GC bid.

No where in the contract does it say that the cost will change without notice.We get the final invoice and it is $3000 (35%) over the estimate price with a note saying the job took longer due to roots on the property.

For example, if you prepay a three-year subscription to a trade journal, the cost is deductible over three years (not just one).2) Work Now, Bill LaterInstead of sending an invoice immediately so you'll receive payment this week, consider waiting until next week.

File that with the Invoice and warranty info.

One of the contractors send us an invoice half a year later with a 7 day payment period.