But they should not be allowed to fruit for at least the first season to allow strength to be concentrated in making a good root system. Often you will get flowers the first season because the buds are already formed but you should avoid the temptation of allowing any fruit to develop. If you are buying apples make sure you get two that are recommended pollinators - they need to be in flower at the same time (there may be a suitable one in a neighbour's garden!) If you Google Apple pollinators you will see several sites that give you information about suitable companions.
Best not to bother with pears if you are in a hurry as they can take a long time to start bearing.

Stera is correct about pears - it's typically ten yeas before they start to bear fruit. Mine took 19 years!

Buy by all means, but when you get them home, don't plant immediately - leave them in their plastic wrappers and stand outside, perhaps against the house wall, for a couple of days, then pull the plastic down for a couple of days to try to harden them a bit before you actually plant out. Assuming the roots haven't dried out for too long in the wrappers, they should be fine.