HCA: Hermit Crab Association

So I bought ~300+ shells off of a previous hermit crab owner on Facebook marketplace. The problem is the shells have this perfume smell inside that I haven't been able to get rid of. Two rounds of boiling water, soaking in isopropyl alcohol, a 48 hour long soak in marine salt water, and leaving them out in the summer sun for a week barely made a dent. The sun did help get rid of the smell on the outside of the shell. Despite an attempt at reorienting the shells, the sun couldn't reach the inside. Shoving a uv pen light inside the shells helps a little bit, but there are +300 shells. I've been hesitant to use vinegar because of its potential to ruin the integrity of the shells. However if it helps, I'm open to suggestions on how to properly use the vinegar. If anyone has any ideas on how to get rid of the smell on a large scale please let me know!!!! I'm a new hermit crab owner and I can't afford to throw away these shells

Honestly, I'd just let them sit out and air out for an extended period if at all possible. That may end up being enough. Vinegar, being an acid, is going to dissolve the mother of pearl interior leaving them rough, which means the crabs will be much less likely to choose them and can potentially cause a lot of damage to the shells.

Someone needs to check my chemistry on this, but hydrogen perxoide should be shell safe (calcium carbonate) and could potentially break down any odors. I've not heard of anyone trying it though. Bleach at proper dilution (being basic) is also shell safe and doesn't leave anything harmful behind for the crabs once fully rinse and aired, it's how shells are prepped for sale so there's no rotting snail smell left.