The general idea is to encourage people to swap clothes rather than buy new ones as this is better for the environment. Swapping sports clothes & gear will hopefully help parents financially too, as it can be very expensive to buy new kits every season (or more often!) when the kids grow so fast.  clothes are not generally sold at the swaps but if somebody happens to stumble upon our event unexpectedly, we allow to take an item or two and come back with something else next time. 
We ask all clothes and gear to be clean and in good condition, we limit 5 per person to keep it manageable.