@Doodledog I was meaning volunteers paying the going rate for an item. Or maybe a small discount, as others have said there can be a monetary cost to volunteering, parking for example. As a hospital volunteer you get parking and a small amount towards food in the canteen if you're there over dinnertime. There is a push to involving many people v to volunteer and it is recognized that if there is a cost to volunteering this puts some people off as they cannot afford to spend money to volunteer but they do have time to offer and the perspective of a different part of society maybe. Covering expenses of volunteers is a sign of a well run charity. If someone doesn't want to claim them no worry but they could take the expenses and gift aid them back as a donation, www.ncvo.org.uk/help-and-guidance/involving-volunteers/planning-for-volunteers/paying-volunteer-expenses/#/
Although I love looking through charity shops, and often find lovely things in them, I also often look through them and find nothing nice that will fit me, no interesting books, no household or crafty items so don't buy anything. It's going to be like that with volunteers, sometimes there will be things that volunteers might be interested in, many other times there will be nothing, all wrong sizes, colours, styles, ugly ornaments. I am not sure that volunteers buying things is a big problem
Helping in a shop is not my thing, but I have helped at many a jumble sale or bric a brac stall at a fete. Volunteers on those sort of stalls always have first dibs on things, for a fair price obviously, never heard anyone complaining about that. Always plenty of stuff for the public, on the other side of the table I clothed my children from jumbles etc