is there was a way to control/customize the number of items given out after one purchase? 

At this time your only option would be to set cooldowns in the config for either buy and sell or both so that when 1 is bought it starts a cooldown before they can buy that item again. A limiter function is in the works but is being delayed due to a core design flaw that I am still working on fixing in the next update.

Ah ok!