I act like a self-appointed price monitor at my local charity shop (here they’re called Opportunity shops, or Op shops).
I’ll often bring things up to the counter and point out to the manger if they are wildly overpriced or underpriced. They appreciate my input, and usually change it on the spot. They can’t all be expert shoppers like me 
I’ve built my reputation with them over the years- they know they’ve made far more money with my suggestions. Turnover is more important than ever, people aren’t going to drop in if it’s the same old tat for ages.
I’ve often thought that these shops have a very narrow idea of retail strategies. They think they know, but they don’t. They don’t need to be ‘more corporate’, they just need to cherry-pick the retail strategies that work in their community and actively reject the rest.
I’ve convinced them, for instance, to put aside costumes and display them prominently twice a year- before Halloween & book week. They sell out this way, and got more costume donations. Word gets around the local school, and people who never come in, come in for that rack. Previously those costumes were distributed in 15 different places, according to size, colour and a bit randomly!
Now when the staff see ‘demand and supply’ in action, they can charge a little more (briefly, and for some things). Leaving the ‘daily basics’ for the bargain-hunters and people doing it tough.
Overpricing is a very backward-thinking move. And quickly earns the shop a ‘don’t bother’ reputation in their neighbourhood- both for donating and buying.