How do you 5 day old chickens???

I just bought 4 baby chicks, and the seller couldn't tell us what they were, but my husband wants to know for peace of mind. Ive tried the feather ing, but the pinfeathers have grown out a little bit, just enough to not be able to tell. And to be honest, im a little weary of poop flying out at me when i look at the vent. None of them are full blooded certain breeds either, so IT'S DIFFICULT!!!