I just posted this on another thread today. My fridge cart allowed my previous TAF to get released down my stairs like a locomotive, taking out the railing, wall, and smashing to shit at the bottom, almost killing the guy helping me... someone I met here on pinside too.
Since then, I have started strapping the bottom of the cart, across the neck of the cab. I've thought of welding on an extension to the bottom plate as well, but it doesn't move at all now with the extra strap.
I STRONGLY suggest another strap is used on these. I must have moved 60-70 of these things without issue, but the guy buying lifted the rear over the top nose of the stair too much (my error, as I just said lift up, when I should have clarified just enough to clear the nose) and lifted it high enough to allow enough movement with the single strap built into this cart for the bottom of the machine to clear the bottom plate. I was in complete shock after.
NOT a happy day that was... Yes it's repaired, and he still bought it after, and the least amount of damage and no injury that could possibly be dreamed given the situation. Literally a miracle.
Don't let this be a possibly for you, strap the bottom of these things!