Hi, Linda,
By "pop-up" charity shops, I think that Rick's writers meant charity shops in general. All of them have permanent locations. We visit them every time we're in Inverness. There are so many that it takes half a day just to visit the centrally located shops.
The best that we've found are the Highland Hospice in Falcon Square, the OXFAM shop on Lombard Street, and the Blythswood on Harbour Road.
Since our last visit, it appears that there is a new Highland Hospice shop on Harbour Road. That and the Blythswood shop are a bit removed from the center of town, but close enough together to make the side trip worthwhile.
Shop 'til you drop!
Mike (Auchterless)