FedEx frowns upon shipments of cash. Just sayin’

Also, don't forget that Garmin will sell the same unlock as a download to the dealer. Different part number, same price. You download the file to an SD card you supply, and then it becomes the same as the physical card you could order instead.

For example, the 3rd party radar A708 enablement for the TXi series is available as a physical card P/N 010-01477-4D

OR the downloadable file P/N 006-D7010-E0

Bitcoin (or some other cryptocurrency) is non-censorable. (But it is traceable). If you have no evidence that the seller isn't legit, you could pay that way.