If you want to make it really interesting, how about two customers fighting over a single plant? Either the plant would be knocked to the floor and die on the spot, or a bidding war would break out, bringing a handsome profit for the store.

And then introduce the occasional (very rare) shoplifter. If you aren't vigilant (rather than dashing off to check email or make a sandwich) you could come back to an empty plant stand and lost revenue.