What do I do next to remove this sofa stain?

Hello (she wrote casually, after a nearly 10 year hiatus),

I am selling a purple sofa (100% polyester, no slip cover) but I noticed some old brownish stains on it. After some googling, here’s what I tried:

1. Used the iron on steam setting to try to loosen it
2. Used dish soap in cool water to blot the area, then went over it again with just water
3. Dried it with a hair dryer

After this the stains were pretty much unchanged.

4. I sprayed Shout on them and rubbed it in with a toothbrush. I let it sit for maybe 45 minutes, and then used a cloth with water to remove it. It was very sudsy and I regretted the volume of Shout used. There was a brownish residue on the cloth (the stain was brownish, so that’s a good sign?)

5. I let it dry overnight. Today, I don’t see evidence of the stains, but there are large “water marks” around two areas and it looks MUCH worse. Not sure if it’s Shout residue or stain residue or what. They are dark (not the color of the stain).

The part inside the main area of Shout-ing looks really clean and nice and smells great!

So I think the Shout worked but maybe is still there? Or did it just push the Shout out? I lost one buyer when coming clean about this (no pun intended), and there’s a second one who could come tomorrow but I want it looking great.

I don’t own a carpet cleaner and would like to not invest in a whole apparatus. I can buy a product, though.

Surface is 100% polyester, filling is 45% pocket coils, 35% polyurethane foam, 30% polyester fiber.

Thank you! Too bad I can’t attach pics!