As a rule, you're not supposed to have them i don't think - when we visited Aalsmeer market they told us they should all be sent back to them, where they get washed out on a big conveyor thingie then re-used. The wholesaler is charged for them with the deliveries, then gets the money back when they are returned - so if you 'accidentally'(!) keep a few with your flower delivery then they are out of pocket.
My wholesaler (Van Vliets) have recently started charging you if you take them (about a fiver), then refunding you when you bring them back & have said if we need to buy any for peak periods etc then we can do - so your wholesaler might sell them to you if you ask??????

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