I took my Fiesta ecoboost (100) for an air con regas and clean today. 

On collection, I was told that it was overfilled, he showed me figures of 70 something whereas he said for my engine it should be in the 60s, again not sure what he was quoting, they might have been 100s or 1000s.  Anyway, he took out gas. I've never had the air con serviced and having bought the car at 18 months old, I doubt it has ever been done.

Having driven around all afternoon, the car doesn't seem to be as cold as usual, to make sure it's not in my head I bought a themometer, stuck it in the vent, put the air con on in recirculate and found I was struggling to get below 50F, apparently the temp should be between 40 and 45 degrees F.

Could someone tell me what figures he is talking about?  Is there specific amount of gas/ pressure for different engines?  If so, where can I find it?

I also paid for a bacterial clean, I'm taking it I would smell it, if it had been done (having used the Halfords DIY ones before), because the smell in the car was exactly the same as when I left it.

I consider that cleaning thing to be a bit of a joke. I take it your car had refrigerant already in it, and it was a case of swapping it? Perhaps the guy was saying the owner before you overcharged it? Everytime I have used refrigerant, we weigh it in and out in kg. That way you know if something is wrong, there will be a spec sheet for how much somewhere. Therefore, yes there will be various amounts depending on what engine you have.