One of my tenants is in her upper 60's, she works for a temp agency and has difficulty paying her bills.  

It's run on an agreement between two parties and if those two parties have difficulty agreeing then negotiation begins.

It sounds to me like you already know why what you're doing is difficult. I

My concern is its narrow already and putting a permanent baluster setup is going to make maneuvering furniture around the corner even more difficult.  Is

My deal went off without much difficulty. 

There could be some distressed property that a Realtor has listed where they can't get it sold and would work with you, but you'd need to know how to deal with them.You can just skip the basic stuff and head on out, follow some guru or wholesale mentor program, take the low road, bump into problems, have more difficulties, step in it, get pie in your face dealing with other professionals, maybe get a bad reputation and be avoided by others, end up messing over some homeowner, for a few years learning by trial and error, or, you could begin by studying where all the professional types begin and avoid all those issues.

The ADA defines undue burden as "significant difficulty or expense".

Instead of seeing the inconveniences/barriers/difficulties as points of frustration, it could be more helpful to remind yourself that this is why income-producing real estate is such a great investment.

DEFAULT BY BUYER: In the event Buyer should fail to consummate the transaction contemplated herein for any reason, except default by Seller or the failure of Seller to satisfy any of the conditions to Buyer's obligations, as set forth herein, Seller shall be entitled to retain the earnest money deposit, such sum being agreed upon as liquidated damages for the failure of Buyer to perform the duties and obligations imposed upon it by the terms and provisions of this Agreement and because of the difficulty, inconvenience and uncertainty of ascertaining actual damages, and no other damages, rights or remedies shall in any case be collectible, enforceable or available to Seller other than as provided in this Section, and Seller agrees to accept and take said deposit as Seller's total damages and relief hereunder in such event.

By asking good questions, you can uncover their real motivation for selling.3) Once you've uncovered the real problem they're trying to solve (maybe the mortgage payment is too much, they lost their job and are having financial difficulties, or the maintenance on the home is too much, etc.), constantly present yourself as the solution to the problem, ie, "sir, I can understand how all the maintenance issues can be overwhelming, so how would it feel to walk away from the home with a big check in hand in a matter of days?