Aww, why'd you give them to the pet store?
I'd always be afraid to do that- I wouldn't be surprised if a lot of the people that come in pet stores to buy birds (or any animal, really) usually aren't ones that do a lot of research and end up putting the finches in tiny cages or feeding them seed-only diets and similar unfortunate things.
They don't incubate their eggs until their clutch is complete/nearly complete. How often do they lay eggs? If it's an every day occurrence, you should consider letting them brood because laying so many eggs is draining and predisposes them to things such as egg binding.