A user can assign multiple manufacturer rebates to unit. This feature is available in Astra and G2.
To Assign Multiple Manufacturer Rebates:
In G2 Sales> Unit Inventory> Maintain Units, select any unit with Status of Available. On the Cost Information tab and left click on the Mfg Rebate field and a new window will popup Manufacturer Rebates, which allows entry of multiple rebates from multiple manufacturers.
See the example below: