Heilongx

I brought some Katana CR5 rims and wheels from http://www.talebtyres.com.au/ The guys put inserts in, buy they are not flush with the surface, they sit few mm below. I went to Bob jane, Jax Quick Fix, they both wouldnt put the wheels on, saying, "Rims could fall off when you drive" Jax Quick Fix said, "people do put inserts in, but they should sit flush and not below" My question is, are inserts safe to use on rims, is it common for them to sit just below the surface Thanks