Upload & Sell: Off
By default, all SDXC cards come formatted with a proprietary Microsoft file system called "exFAT". Apple didn't start buying exFAT licenses from Microsoft until MacOS 10.6.5, so older Macs don't have exFAT drivers.
SDXC cards are relatively rare. I don't think any manufacturer sells SDXC cards that are smaller than 64GB, and not all big SD cards are SDXC. If you gotta use SDXC cards, you can either re-format them to the more common FAT32 standard, upgrade to a newer version of MacOS, or use a Windows computer.
But, you're using your SD cards for JPEG backups only, right? Do you really need more than 32GB for the JPEGs from one wedding?