if he laid them on spots, they will crack, if he laid them on a bed of pug you'll be fine. lift a slab up to see what he laid it with, then stick it back down by putting some 'no more nails' on the existing pug bed
if he laid it on a sharp sand screed then you're likey to get channelisation which, depending on the size of the slab, i'm assuming 600x600, is more likely to cause cracking and an uneven surface and a shit looking patio.