A random question you can ask your tile contractor is this.
"What is the best thin-set to use and how fresh should it be?"
This is a good question and can lead to many different answers. Most tile pros have a favourite but tile choice will play a factor. Also any tile pro not familiar with checking his product for freshness is a RED FLAG in my book.
Thin-set is always on the move. Pallets come and pallets go. Not knowing how to check can put some expired setting materials into your shower's build and this one error can result in a failure. I've been there and done that. This little School of hard Knocks training has hit me hard in the wallet when we needed to redo an entire kitchen floor's tile!.