Personally I'd probably say nothing, in general, but is sounds like you should say something for his sake (plus he can revisit to rectify if possible). I've heard a lot of stories of friends/family doing work which is shoddy, especially if the payment was 'mates rates', quite sad.
We bought some fired earth glass mosaic tiles when I replaced our bathroom, as they cost £400 PSM I got a pro in to do them, he did a crap job in terms of the finishing (edging work mainly etc. The main body was OK), but as our house is old it doesn't look to bad, but considering the guy was showing off how he'd done work for elite names it was crap, he was from checkatrade but it wasn't bad enough to slate him, just not good enough to promote him. If I do another bathroom I will do it all myself as most tradesman are not worth the salt from my experience, in terms of finishing (I did all but the plastering and tiling, have since done a plastering course and will give the tiling a go as well in future), unless you get an outstanding craftsman.
It sucks, especially in the current environment that you get anything less that outstanding work for your money. These type of things are your high shelf items, that when you splash out on them you should feel really happy with it at the end (unless you made a poor choice of materials of course). One thing I've learned is to never let the wife be the one around to supervise, mine is to easily swayed by trade flimflam.
Edit: just saw your reply above, if you told him before, I'd get someone else to touch it up (if it's only grouting and it's not in your skill set). As Rab's said it's probably why he's not getting work.