They visited the house as part of their due diligence but I never heard anything further from them regarding any concerns they might have.  

I have equity in my property which is in Washington state, and I'm interested in finding an investor who would be interested in loaning me 20k to 30k in exchange for an agreed percentage rate when the house sells (within 10 years).

Land only and not houses.  

Motivation is to overcome down payment hurdle for expensive houses for STR

Besides private websites controlled by the brokerage houses themselves and the MLS, there isn't much left.

While MLS remains the primary platform for on-market deals, the majority of deals I encounter originate from off-market sources, often through wholesale channels.When you say wholesale, someone(wholesaler) finds a homeowner who is in need of cash quickly or cannot go through traditional process of selling their house for some reason, and then the wholesaler finds an investor to buy the house who will pay in cash? 

My original plan was to rent out the space to Section 8 tenants, but from my experience so far, dealing with Baltimore City housing and inspections can be a serious pill.

Housing inventory in Austin rose to 5.4 months, which is over one month higher than the greater metro’s 4.3 months of inventory.

"turnkey" companies are basically just a combination of in house investor realtors and property managers working in the "turnkey" markets.

I think the trouble I might have with that option is the current condition of the house.