When we purchased our laundromat, it had a strong brand and positive reviews online.

Sounds like this property is better suited to be a LTR.You will likely get some unfavorable reviews about the neighborhood that may make your decision for you.

But... what I need to review is how this is achieved as I would benefit from building the new unit as an ADU.

AirBNB and VRBO don't transfer accounts and reviews.

This could add some credibility to your reviews and recommendations.

By reviewing sponsor after sponsor, and deal after deal to uncover what sets apart the good from the bad. 

Long story short, you can, but since you are only targeting investors, your sale price will likely be lower than comps.Talk to a local agent about your local tenant laws and have them review their lease

It got great reviews and everyone said it's working for them.

They had good reviews so I am planning on working with them and seeing how it goes.

So when I'm reviewing screening reports for my rentals, I like to find out the story behind an eviction - I've had good tenants with evictions on their records who never bothered to expunge their eviction from the record when they had a prior vindictive landlord (yes, such landlords do exist and give the rest of us a bad name).