However if I do a BRRRR I can achieve infinite return by extracting all of my investment.

Yes, the $50k is only a 31% Tax free ROI but being that we got 100% of our investment back, and we still own the cash-flowing property (that we plan to keep forever) everything that we make from that property moving forward is an infinite ROI which is “Created money” (not earned money).

I do not have the skills to determine ROI on properties were all the initial investment has been pulled; is it an infinite return at this point?

If you're financing 100% of the deal, your COC will be literally infinite, because you have no money in the deal.

What is a good ROI for a BRRRR? I know people use CoC which is great but if I am getting 100%of my money back out, how would I calculate a good return? Here is the info on the potential property:Purchase- 50kRehab - 3...

This way you can put a short shelf under a deep shelf. 

If you focus on creating more money/income you’re dealing with a potential number that is infinite.

You want to have a tax strategy, diversify (maybe some syndications, self investing in RE, whole life policies for infinite banking, some stock market,  possibly buy existing biz with great operators / operations and just keep them successful, etc.).