How do those "we buy gold" storefronts work? Do you really get fair values for your stuff?

Not far from where I live, two of those “we buy gold” places have opened up. (I think there used to be more when gold had a higher price, but ..)

I’ve never been into one of these and I only own one thing of gold, but I am curious about how these places work.

My assumption is that they have scales and weigh your jewelry, somehow take into account the purity of that gold, and then make you an offer. But is their offer based on today’s gold price? Or is based on some (less than generous) pricing scheme?

Other than to get quick cash, is this a fair and honest mechanism?