I, as the shipper, tell you (the receiver) out-of-band that you're getting a tilt indicator with serial #C097412. You check the received label against my out-of-band signal to ensure it matches.
Assuming the warehouse worker can afford all that, someone offering anti-tamper-bypass-as-a-service is going to run headfirst into the FBI, SCA, and other well-resourced government organizations with which a sane individual would never consider fucking. That does not lead to rising property values in Tokyo.
Tilting packages doesn’t seem particularly fun or lucrative. It’s not even a particularly effective form of sabotage: maybe you’ll increase the damaged-in-shipment claims by a bit, but maybe not.
If you’re already forging and breaking into wear houses, surely you could find something more enjoyable, profitable, or vicious to do than provide post-hoc cover to a rough shipper.
You are a delivery worker. You will get fired if you aren't fast enough. You will also be fired if you trigger a tilt indicator.
You're on your final warning, and replacement tilt stickers cost $3 on ebay.
A delivery worker won't be hacking e-mails - but if they know hardly anyone checks the tilt sensor serial numbers anyway...
I have no idea how much such a service would cost (perhaps your life is much more exciting than mine), but I'd imagine skilled forgers don't come cheap, as they could easily find something more profitable to do than faking tilt indicators.