If you are getting the same response from more than one professional, then it could be that you are not communicating well.
Maybe your wish list needs adjustment.
(Please note: when you choose an answer as a Best Answer, or at least give a thumbs up, it helps those who answer questions here.)
First no agent should not show up to a scheduled appointment and I am sorry to hear about your difficulties and fustrations.
Finding an apartment can not always be an easy task.
Most agents will over the phone try to qualify you and your expectation and based on your responses the agent will likely know their ability to assist you based on their knowledge of the inventory and landlords requirements.
There are many things that come into play. How many people is it for? Any pets? How many childeren if any? What size apartment are you looking for? Do you have a car? Are you prepared to pay a first months rent and security deposit? Some apartments require you to pay the agents fee or 1/2 of the fee? When do you need it?
There are agents in most of the Newton offices that specialize in rentals and as stated by Masha, manyof the listings are open and not posted on the mls. I do not but email me and I'd be happy to give you the agent in our office who does. I do have one possible rental, but it is in West Roxbury off Lagrange St at the Newton, Brookline line.
Craigslist is also an excellent place to look but be careful as there are scams out there.
I suggest you try to find someone that will really listen to what your needs are and has suggestions that really meet your needs, as opposed to showing only the listing that your responded to. Many times, it is not the right property, and if the agent has an in house inventory of listings, they could browse them with you and find the right match. This will only happen if they are listening to you, not just try to show you something. I work with Masha, who also answered here, and can recommend her highly as someone who will do just that-listen first, and show only if appropriate, but then will go find it if its out there. Let someone else do the scouting for you. Rentals are a bit of a tangled mess, er... web. Good luck!
do not let the experience you have had with a couple of agents discourage you. There are plenty of great agents and brokers who would be happy to help you find a rental, as mentioned here. Good luck