I would add that I would wait until the chicks look completely stable for at least a week...everyone should be perky, fully fluffed, no hint of diarrhea....before attempting to sell.
Coccidia live in the environment and stay in the gut pretty much permanently. The flora of the gut keeps it in check as does the bird's immune system. And as the others have rightly said, that takes time to develop in little chicks.
For any bird, it is during times of stress which lowers its immune system such that an outbreak can trigger, or during times "ripe" environmental factors create enough build up in the environment that a bird's system is overwhelmed. That is not hard to do with the immature immunities of chicks...which is why the industry typically keeps them on medicated feed so that their bodies can have time to strengthen without coccidia overload. (Medicated feed merely keeps the numbers in check as the Amprolium is pretty low. Corid or Sulmet drugs will eradicate, for a time anyway, an infection).
All to say, moving to a new home too quickly might trigger an outbreak, so I would give them at least a week of solid perky health before selling and injecting more stress onto their systems. They are going to need strong systems as likely they will have to get used to another strain in their new home, most likely. (Each farm can have different strains, even across town or the neighborhood.)
If you aren't doing so yet, after the meds, put them on apple cider vinegar, raw with the mother, and probiotics. That can help balance the gut to keep the coccidia in check.
I would tell the new owners to keep them on acv/probiotics and put them on amprolium based medicated chick start for at least the first month, two being better, to help ease the transition and prevent a flair up.
As a purchaser, I would want to know that the chick is not going to get sick shortly from the stress of the move. I would also tell the new purchasers that any new bird, chick or older, should be in isolation for at least a month as a "golden rule" with any bird brought into your place.
My 2 cents.
Edited by Lady of McCamley - 12/4/15 at 11:33pm