Does anyone have experience with filing a lien (at least I think it's a lien) on a property with a private mortgage in Prince George's County?

IF they are only selling a lien then the tax sale may not be an issue.

Of perhaps get some answers to the following:Im concerned about the contractor finishing on time, making sure I only pay him for work that has been performed, and not work he has yet to performmaking sure he is liable for work performed which isnt satisfactory,making sure he performs all the work we agreed uponensuring his workers are insured, licensed professionals.Id like a termination clause if he fails miserablya written lien waiver upon full paymentAnd im wondering about how to handle it when things (inevitably) go wrong.

Outstanding to set a goal and accomplish it!  

You might get stuck with a project you can't get permits for because the city slaps a lien on the property for work done before you owned it.Not saying that's the case.

The home has WELL over $500,000.00 in outstanding debt that would have to be satisfied in order to gain clear title. 

First lien is foreclosing.  

There is a subordinate (2nd position) lien of $49k.  

Tax Lien / Deed expert for South Carolina.Most of my house have been aquired through tax Auction for pennies on the dollar.I also invest using my self directed to Roth IRA with checkbook control.

 $100/door with a DP of $500 in the midwest sounds outstanding.