I’m not saying you can get SBA financing over a owner finance deal. You really need to talk with a lender that does these loans. Generally speaking, a person with experience in a given area, like laundromats, can get a SBA loan with 10% down. In some cases they will allow gifted funds or small loans from other sources. This is on a case by case basis as EVERY LOAN SITUATION IS DIFFERANT.
I have two SBA loans but this does not make me an expert by any means. The situation with my first Laundromat that I referenced above, this was not a SBA loan.
The correct answer will be when you pick up a phone and call a lender and hear it from them. Eastern finance is well versed in the area.