Bead sealant sorts this problem out, unfortunately not all garages are using it. Most of the mainstream garages I've used, suchs as ATS do a horrific job of tyre fitting and don't use bead sealant, so my tyres go flat quickly. I've since found a local small garage who use bead sealant. Although they're not the cheapest to buy tyres from, they fit them properly and you'll not need to go back to get a leak sorted.