I'm with JP on this. Most homeowners will empty a couple cans of raid on the returning foragers and never get any active where it counts in the core of the brood nest.
Being truthful here I have killed enough bees to say that even with the dusts (delta, drione, sevin) and a good bellows or bulb duster it is hard to get a quick and complete knockdown unless you really know how to access all areas of the comb. Even foggers are not as effective as one might think. The lllllllll of the combs leaves the center combs (always covered by bees) pretty well protected from assault from without. Now the dusts are particularly pernicious as the bees themselves will track the dust into the center of the brood nest, just don't expect instant kill. This is why many turn down these jobs as the bees are dead ladies walking.
Consider, too, that in any healthy colony there will be brood emerging in the hundreds on an almost daily basis so a homeowner can knock down almost the entire field force of the colony just to have it replaced in very short order. It would take a weekly dousing over the course of a season by the typical homeowner and a can of raid to eventually crash the colony. Use your judgement and get as much information as possible. If, in your opinion, the exposure has been minimal to the brood nest and you can get them out asap (to minimize tracking in of toxins) and get them onto clean comb then go for it. They may be sick but if exposure is minimalized they will pull through.
You also might want to take your beekeeper hat off and think about this from another angle. Yes, as a beek you want to save the ladies and bring them home to make you some money but think of a removal as just that, a removal. Screw the bees, get paid for the removal and if the bees make it then it's a plus. IMO you should always get paid more for removal of bees that have been treated as there is no guarantee of profit from honey later on.
In my line of work it's the same as if the homeowner has tried to trap his own beaver or been taking pot shots at them. I'm there for the removal, if the homeowner has educated them and made my job harder then I charge accordingly.