The thrifts here will test some things but not others. If you buy something and it doesn't work they will let you exchange it for something else, but that can be a pain if you don't find something else for the same price. The Salvation Army has stickers on the appliances that read something to the effect of sold as is, not guaranteed. Always best to plug it in at the store if you can.
That's kind of scary that thrift stores put up used electrical merchandise that they either haven't tested or they know it doesn't work and could cause a hazard to a potential customer thinking of buying it or did buy it and found out the hard way it doesn't work.