Milly, you should not have to Know what to look for, when you employ a professional you should be able to trust them to do the job correctly.
Much the same as I trust the mechanic who services my van, I, along with I'm sure my fellow members are gutted when we hear stories like yours. You pay for a job in good faith, and expect a top class job. This guy is not a tiler, and the law should come down on your side.
Another example why trades should be licensed imo. I again hope you get this resolved with no cost to yourself, I wish I was in your area I would love to put this right at a discounted rate. I hope this so called "tiler" gets his just rewards, sorry to go on, but I have spent a lifetime trying to do my job to the best of my ability. Good luck