Plumber thought faucet was bad; no water came out of moen

There's a clog in the shut off, line to faucet, or in the faucet cartridge ... hook it up to a supply tube on another faucet, it connect to a garden hose to check if faucet is problem.
Water pressure problems on following link:
http://waterheatertimer.org/Low-water-pressure.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

My first suggestion is to have the installation plumber return to adjust the faucet to function properly

There is probably junk in the lines that has clogged mixing valve Moen is pretty simple to operate and maintain, however, before the new system was installed, maybe it was done, the water should have been run through the valve itself, without mixing valve installed. I am going to provide you with a video that shows how to remove the valve and, with a little help, you can remove valve and hopefully can clear the lines by running water, slowly, through the fixture, without the valve installed. You would want to try this anyway to make sure you have flow to the faucet:
http://www.youtube.com/watch?v=J-SNBNijfQc
Make sure all junk is cleared from lines and re-install your valve. If your cold and hot water is backwards, remove the valve and rotate 180 deg. and re-install. You can note the way the tabs are when you remove, and install in the same position.

There are several products that can be used to loosen the corrosion holding the handle in place. The Works is one product along with CLR. The easiest fix is to wrap a washcloth soaked in distilled white vinegar around the handle. Let it soak for 20 minutes at a time. It could take a half dozen times or more, but eventually it will work. Rinse the faucet after each application to remove the acid. You may also need to use this process to remove the Moen faucet cartridge.

Not unless you had a backward plumber , If the diverter at the faucet is open for tub, then no water will go up the shower, The shower may hold enough water up there to make it look like a drip, Even if the valve was leaking all the time, it would not go up, it would come out the faucet. It only works with pressure. Unless the valve was plumbed wrong,,, Hope this helps.

If water gets cold at all fixtures Its most likly the dip tube in the water heater they make replacement dip tubes but the water heater usally dosnt last but a yr or so after the tube gos bad. If the problem is only in the shower its probibly the shower valve.It could be a fixture capped off wrong, or water lines crossed som where in the shower end of the biulding.

Single or dual lever? A new ball if single lever. Home Depot or Menards will carry them. Teflon tape if dual cartridge. Stay away from moving parts

The plumber soldered in the faucet without removing the cartridge, the o-rings are melted. Have the builder replace the o-rings.

take out the cartridge and flip it over.

take out the cartridge from the fixture and make sure it has all of the "O" rings and stoppers.
look at the instruction again, make sue you are installing it the right side up. if all that, the shower still leak, then you need to talk to the place you brought the fixture, it may have a defective cartridge.