If they are not licensed, it sounds like they might be guilty of criminal fraud, in which case, they might have skipped town with your money, not just have done a bad job.

Does anyone have experience skip tracing for a whole building?

If you get someone unreliable in there (which these units tend to attract), you will have skips, lates, and a poorly taken care of "shop" costing you hundreds (maybe thousands every turn).  

Don't try to skip the fees by setting up a "personal" account instead of a "business" one; they know about that trick already.It would also be possible to have your own site for listings, applications, etc, and then link the tenants to a service like Cozy to make their payments.I don't work for any companies mentioned.

But i just walk up and knock. if no one answer I run the address on skip trace.

It is simple and very cheap to skip trace them in white pages or county records and send them a card, give them a call, and quite simply ask them if they are interested in getting on your buyers' list.

Turbo skip for skip tracing your data- 15 cents a recordPULL NON OWNER OCCUPIED PROPERTIES AND YOU CAN ADD OTHER FILTERS TO SLIM DOWN YOUR DATA

I was able to find property in my price range, skip an FHA and do conventional with 5% (I thought it was going to be 3.5% but then they said 5% because its a modular [I own the land though, no lot rental]).

I just learned about it yesterday but that seems to be what you're thinking of (if you're talking about skipping the rehab)

Skip the tax for now until business generates enough income.