The market appreciates 3% per year.Pay cash for one house and rent it for $1,500.

Furthermore, @Dave Meyer has a YouTube show/podcast on market trends for your reference.

The seller is so pissed off, he can't wait until Friday to snatch up my $10 gs and put the house back on the market.

The guru your son is learning this technique from is likely not telling your son that the deal will almost certainly encourage your son to get an "off-market" deal from a "wholesaler" who is unlikely to properly disclose the details of the property or encourage an inspection. 

Your focus on the Dallas market and Fix and Flip projects sounds solid, especially with the DIY approach and having an interior designer on your team. 

I also practice as a Realtor because I enjoy it and it is extra income.So as an investor, your options are to get your RE license and have access to a lot of tools and do the research yourself (therefore you're paying with time, energy and a little money) or you work with a great realtor/investor in the specific market you're looking into.

DSCR loans are based off of down payment, credit score and either actual or market rents so it helps to supercharge an investor's real estate goals and net worth.

Any development work they've done on the property also becomes your property.If the property becomes yours, you could try to sell it back to them quickly and below market for a nice profit.

Look at their marketing strategy.

I do not have 5 layers of management that make my rates higher, no lender I work with pays for my office space, licensing, benefits, marketing department, compliance department....