On paper this may look like an obvious solution, however, in practice it can cause more challenges (cost) than it saves for most situations.

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).

I don't understand how a real estate agent would get access to "investor-worthy deals" when I would think the people they work with aren't in a distressed situation and are looking to sell for a profit. 

Yes, there are ITIN DSCR lenders out here for $100K and up DSCR loans.More info on DSCR loans:DSCR loans won't use your income to underwrite the loan.

For illustration purposes, the majority of investors who post on BP will move the property that pencils as a true BRRRR to the front of the line over the better situated asset with better fundamentals merely because they receive 100% of their invested capital back as opposed to 90% (again numbers are merely to illustrate a point).

Right now with higher interest rates you'll have to get creative with financing, like rate buy down, seller finance, or assumable loans.

You may be able to go and view the property as well, depending on the situation.

There are definitely situations where selling to a wholesaler is someone's bets option, but they're the exception, not the rule.

The easiest way would be to leverage a DSCR loan.

I want to house hack the next 4plex with a conventional primary loan using 5% down.