Ask how they intend to pay for a year or two of rent.I ask for a statement of assets and discuss any red flags or ambiguities with them.

Without getting too deep into the weeds, there are a few ways to do this, including:- write up an assignable lease and an option to buy which the seller signs, then assign the lease and option agreements to a tenant-buyer.

The second property, I’m in deep trouble.

Add in property manager, repairs/maintenance, CapEx, vacancy etc and you will be deep in the red.

Are there any red flags or challenges specific to this neighborhood that I should keep in mind?

Basically questions that the PM/co-host need to be able to answer without having to do any deep-dive analysis.Property-specific questions such as property improvement advice, revenue potential, etc. that involve deep-dive analysis might justifiably incur an up-front cost depending on the PM/co-hosts business model.

Is this a red flag, or could it just mean there’s an untapped market here?

And, if they had issues in the far past, it can still be a red flag too.

(and no I don't have friends or family with deep pockets). 

I then look at area vacancies, economic conditions, employment opportunities, area demographics and verify that the property has not been red tagged or have any other underlying problems that might make it difficult to resell or rent.When I have my financial information then I can consider debt service and costs related to equity partners in the overall income produced.