Visit on a Monday morning. That’s when the weekend donations are priced and put out. You get first dibs on the weird stuff. It’s like Black Friday, but with more polyester.
Also, check the jewelry case. Pro tip: sometimes they misprice vintage brooches. You might walk out with a piece of 1960s Bakelite for two quid. I’m not saying you’ll get rich. I’m saying you might feel like a pirate.