I have my brooder setup completely separate from my backyard flock. If the store is giving away the chicks for free, I think I would give it a go, knowing that they might not survive. But, I have had to nurse a chick or two through those first days and most of them survived. If you can stand losing the chicks if they die, if you can raise them separately from the main flock, and you don't have to pay for them, I think I'd try it.
Having said that, I think chicks should be strong enough to survive those first days or maybe they are not good stock to carry. Other than providing heat, food, and water, I don't think I would go to extremes to care for them other than the usual pasty butt type issues.
Last year our local Fleet store got a shipment of weak chicks and many died. I think they just got over stressed in the shipping. Anyway, the store was throwing the dead chicks in a 5 gallon bucket by the display and did not bother to put a top on the bucket. So I asked the manager if he thought that was a good idea because so many little children go there to look at the baby chicks in the store. Also, who wants to buy a chick from them if they have a bucket half full of dead chicks sitting in front of the display? They quickly moved the bucket out of sight and put a lid on it. Too bad they did not have someone there to think of that themselves.