Lisa,
When you book with a travel agent it all depends on who the travel agent is dealing with, either a) the homeowner or b) the MC.
In either case there should be communication between the parties and then with you , the guest,, so that everyone knows what their responsibilities are and where to collect the key from. On your first trip someone messed up. I just felt you were blaming the MC without realising it might not have been their fault!
As regards the keyless entry....I've had problems with those in the past and would strongly urge you to also have a key option. Mount a lockbox with a key in it somewhere else on the house. One day those batteries will fail and you'll end up with a problem !
tmli, one of the other advantages of being with a company is that if the house doesn't meet your expectations, they can actually move you to another property far easier than an individual owner. Of course, if the research is done properly before booking, the chances of this being needed are slim !