People say he might be trying to wriggle out of using epoxy, well he might be doing you a favour. If he's never used epoxy before then don't expect the quality job you want, you will regret it. I've been tiling for over 40 years and I personally would try and talk the client out of using epoxy especially if all the fittings are in (not sure if they are). We use epoxy on large commercial jobs i.e. Swimming pools mainly and have 2 lads who are very good and quick but it takes years of experience to get to that standard, it's also been considered a health hazard and most tilers will refuse point blank to use it. I know we're only talking a bathroom here but be careful you can have a perfectly good tiling job ruined by using epoxy resin grout. There are many grouts available now with all these additives that are compatible with your requirements, but like has been mentioned earlier ventilation and a little maintenance is required.