I’m not sure if it would depend on the shop but it’s really not advisable to bring your own jewelry to a piercing appointment. You‘ll have to make sure that you will only use quality and sanitized metal for your jewelry. Specifically implant grade surgical stainless steel only.
Similarly, is it a bad idea to pierce your own ear?
While I would never say you should pierce your own ears, sometimes it is the most viable option, whether due to finances or otherwise (for an idea: my second lobe piercings at a shop cost $110, while for my third lobe piercings I spent $8 on a 50 pack of piercing needles and $10 on a pair of sterling silver studs).
In this manner, should you tip a piercer for changing jewelry?
For jewelry changing, I keep it relative to the time. Something fast gets a few bucks, something long and arduous gets closer to $10. I usually give an extra $5 for getting gloved and doing a jewelry change done. My awesome piercer doesn’t charge anything, and I tip him at least $5-10 for jewelry changes.