Buying a hot drink at a winter market involves paying more than the drink costs, with the difference returned when the mug comes back. The deposit is a logistics mechanism rather than a surcharge.
The deposit exists to guarantee return
A reusable mug only saves money if it comes back many times. Without a financial incentive, a substantial share would walk away after a single use, and the economics would collapse immediately.
Setting the deposit above the mug's replacement cost would be unnecessary, and setting it far below would not motivate the return trip. It is calibrated to make returning worthwhile without feeling punitive.
Because it is refundable, the deposit costs a customer nothing in the end, which is what allows it to be set high enough to actually change behaviour.
Washing at scale is the hidden infrastructure
Markets with many stalls usually operate shared dishwashing facilities, either in a central unit or in trailers positioned behind the rows of huts.
That capacity has to match peak throughput on a busy evening, which is a serious operational constraint when thousands of drinks are served across a few hours.
Stallholders can normally accept a mug from any stall on the same market, which requires an agreed design and a settlement arrangement between traders at the end of the season.
Waste rules push in the same direction
Many municipalities restrict single-use containers at events on public ground, partly for waste volume and partly because litter collection in a dense crowd is expensive.
A reusable system moves that cost from the city's cleaning budget into the market's operating model, where it is covered by the drinks price.
The visible result is a market with relatively little bin overflow despite very high consumption, which is the outcome the rule was written to produce.
The mug doubles as merchandise
Designs are usually dated and specific to the town, which turns a functional object into something visitors deliberately keep by forfeiting the deposit.
That forfeit is not a loss for the stallholder, since the deposit typically exceeds the unit cost of the mug and the sale converts into a small margin.
Collecting them has become a genuine habit for regular market visitors, and some towns change the shape or the motif annually for exactly that reason.
What a visitor should know in practice
Deposits are usually returned at any stall selling the same drink, but the rule varies where a market spans several squares under different organisers.
Keeping the receipt is rarely necessary, since the mug itself is the token, but a chipped or broken one may not be accepted for refund.
Anyone intending to keep the mug can simply walk away, and no further step is required. The transaction is already complete at the point of purchase.