If the work needs updates, that’s where it can add up, but $30K sounds like a reasonable cushion based on what you’re describing.It sounds like a solid deal, especially if the cash flow is good.

For a $300,000 property it could be $30,000.Then, do you have that much cash or credit available to you, in the event of a Due on Sale call?

Also, if you buy using a hard money lender or cash, Zach Starnes can do re-fi's off the appraised value shorter than the typical 6mos and then you might not need any money down if you buy at the right price.

If you aren't familiar with Baltimore, I would suggest it's a hard no and say that you are trying too hard to make cash flow happen talking Baltimore and tax liens and auctions.

If you're open to expanding your search, Columbus OH also has positive cash flowing deals at an affordable price point - $120k-$180k. 

Many of my customers who are traveling nurses buy condos or townhomes in Florida as vacation homes, then rent them out when they're not in town.This system has proven to be very lucrative, as it allows them to service the mortgage debt and generate a good cash flow.

I know this is above and beyond what most municipalities require, but being fair will make the whole process easier.Additionally, a new landlord can reduce the 60-90-day notice by offering more moving assistance (cash and/or labor) if they move sooner rather than later.

I would restate that the lease will remain in place until such time that a new tenant is selected and moves into the property.This approach will ensure your cash flow while acknowledging that 'stuff happens.' 

I've seen many people suggest a cash out refi but I like the flexibility of the heloc.

So seems like a decent play for cash flow but not much for appreciation.