Actually, several investors (myself included) work with sellers in this situation nationwide--even in cases where there might be some negative equity. In cases where the seller is extremely underwater (has more than 10% negative equity [my criteria]), we might structure the deals using other exit strategies (namely short-sales, short-paper, DIL, or private workouts).
Agents/brokers can--and do--get paid when helping to facilitate a properly structured lease-option. Wendy Patton, Phill Grove, and countless others have plenty of materials both online and offline that explain how to do it. One may also discuss this with an experienced real-estate attorney.
The reason why doing a lease-option might make sense--even in cases where the seller has little/no equity or some negative equity--is that given a long enough option period, the market value of the subject property eventually will appreciate to a point where its appraisal will support that valuation. That's definitely going to happen due to inflation and the continually rising costs of living. While this might sound like a speculative play, it's not. This is primarily a cash-flow play, with a possible equity spread kicker, and a downside hedge (the option).
If the property doesn't appraise for the strike price, then the tenant/buyer doesn't have to exercise the option. Yet, if the landlord/seller and tenant/buyer are happy with the arrangement, then they could arrange to extend the lease and the option to give themselves enough time for the real-estate cycle to catch up to where they need to be.
This play is tried and true. It's been used effectively during several of the other previous down cycles; some of us are using it now too.