When we run our skate swap, it's a one-day event. Skates arrive early; they are tagged and priced, and ordered by size. They are put on tables with people guarding them - to avoid 5-finger discounts.
Then, we set up a central "try on" area with carpet and chairs. This cuts down on damage to the skates and the blades.
We use senior skaters who know what they are doing to ask for skating level, choose, and fit the skates. People aren't allowed to just "grab" and fit themselves; they get assistance, which helps on many fronts, including preventing damage to the skates and theft.
Where there is a question aboiut suitability, we suggest the skaters text/call/go find their coach to ask for direction.
We also keep a cheat sheet of the retail price of the various models and blades so that people have an idea of what they are saving. Particularly good for newbie parents.
Yes, the club takes a cut; it goes to charity.
Skates that aren't sold but are good ones in reasonable sizes: if the parents want to leave them with the club, they are there in case somebody wanders in looking for a pair, and they will be sold on an individual basis.