My local garden centre won't re-use them, as they say it risks spread of disease, even though I would be returning the ones I had used to bring home the plants purchased from them. They do however provide a large crate at the end of their car park where customers can put in used pots and other customers who don't mind using old ones can take them away. Makes complete sense as why pay for new pots in the GC when there is a free supply in the car park! I wash old pots in the dishwasher and they come up like new. A little bit of dirt hurts no one. My wife doesn't know!