you can soak the tiles in warm water and rub the adhesive off the back. tubbed adhesive comes off well like that. but the minute it comes into contact with the air, the adhesive starts to dry, so get the adhesive off asap. will save you having to buy more and more tiles.
OMG I'm no tiler but I think my first attempt is better than that.
I hate complaining I've just had a new builder re-do some work a previous builder did because they made a hash of it. And I wasn't going to give them a chance of knackering it up again. So personally I would just get another( read proper) tiler in.