I have two bathrooms that have been completed in the last year. Both have the same Price Pfister rough-in valve. One is sticky and requires a bit of force to turn on the water (turns on by pulling). It actually has gotten worse over time. The other turns on with a gentle pull of handle. The plumber that installed the sticky one may have pulled out the cartridge and messed it up (rationale: because he messed up other things). I'm wondering if this sounds like something I might be able to fix or should I get a new cartridge? The valve in question is a Pfister 0X9 Brass Single Control.
I have sanded out a few valves before. You would simply remove the cartridge and "sand" the inside of the valve housing. The sanding needs to be even, so try to work in a circular fashion. Just sanding out 1/500th of an inch might get rid of your stickiness. There is some grunt work in this and it takes about 20 mins per valve but has worked on everything I have had issues with. I have had people suggest plumber's grease too. I could never find any and sanding is cheap and non-invasive so I have gone that route.
I would initially treat a sticky valve the same way as a sticky door. You could even sand the cartridge but these usually have ribs in them and I don't know if I would trust myself doing this evenly. However a person with more artistic talent could certainly go this route given that it is faster.