How to calculate how much to pay a tiler?

Question

Currently having my bathroom renovated. 

The tiler just finished. 

Cost is per m2 not hourly. 

So I was just wondering, is how much I pay based on the finished surface area

Or total area of all tiles purchased minus all unused tiles? 

At first I was going to only pay for the finished surface area. But a friend of mine was convinced / persuaded me into thinking   Otherwise. 

All tiles, adhesive and grout paid for and supplied to tiles

Answer 1

This makes no sense. 

You contact a tiler and ask him to quote for a labor only price for the job. He gives you a price. You either accept the price or you don't.

Answer 2

You pay what was agreed upon when the tiler gave you a bid.  Who doesn't negotiate this up front?  And you're really talking about a few scraps/partial tiles and debating over almost nothing.