No. @Delvis has posted a copy of a standard t&c of these companies.
1 or 2 in a crate I wouldnt expect replacing, 18.... yes new crate please.
This is where percentages don't work.
If i'd ordered 20 and 2 were broken (lets say chipped on the corner) then they're more than likely usable for edging or those awkward gaps, and wouldn't be worth the hassle of trying to have replaced.
If i'd bought 100 tiles though, 10/20 damaged would be completely unacceptable. Even more unacceptable is the shop expecting me to add on an extra 10-15% more for breakage.
Notice how they lump in to those T&Cs, breakages caused due to your own fault - cutting/wastage, with those that aren't your fault - damage in transit etc.
In reality, i'd imagine a tile shop wouldn't contest against this anyway, as other posters have said it's more than likely in breach of consumer rights.