Does anyone have a recommendation of a national collection agency that is effective?

Quality over quantity for me. 

I’m about to be 29 and I’m hoping this really takes effect in my life in my 40’s.

How have you identified quality contractors and kept them on pace?

Buyers expect premium finishes, so skimping on quality can hurt resale potential.

For instance, structuring investments through a European company that acts as the buyer of the properties and handles renovations could be an effective solution.

They must provide quality service, or their clients won't want to pay the price.

Buyers expect premium finishes, so skimping on quality can hurt resale potential.

If it's on your credit, you are on the hook for it.However, it shouldn't effect the loan process too much, a simple Letter Of Explanation should be able to get the job done with the correct investor. 

While I don't object to spending money to do one's due diligence, I don't know if $500 is called for when you can get very high quality syndication groups/meetups/information for free.