This kind of monthly code is usually funded fully by eBay so in theory, no jackings.
I tested the code working on stores (e.g. Sony and Dyson) as well as private sellers (eligible).
Conditions. This offer entitles you to a Discount off the pre-coupon purchase price (excluding postage costs) on Eligible Items during the Offer Period. Multiple items may be purchased in 5 transactions per person, including cancelled transactions as set out in the Cancellations clause below (up to a maximum of 10 items per transaction).
“Eligible Items” means items listed at eBay.com.au where a link to these terms and conditions and the coupon redemption code HGTECH1 is found in the item listing.
“Discount” means the amount saved per transaction as set out below:
Save $10 when you spend between $100 - $199 in one transaction; or
Save $20 when you spend between $200 - $499 in one transaction; or
Save $50 when you spend between $500 - $999 in one transaction; or
Save $100 when you spend between $1,000 - $1,999 in one transaction; or
Save $120 when you spend $2,000 or more in one transaction.
Redemption. To redeem this offer during the Offer Period, enter the redemption code HGTECH1 into the redemption code box during checkout . This code cannot be used in conjunction with any other eBay offer, coupon or voucher. You can only use the redemption code 5 times during the Offer Period. Where a transaction for which a redemption code has been used is cancelled either by you or a seller, the redemption for the cancelled transaction cannot be re-used and will still be considered a redemption as set out in the Cancellations clause below. The code is provided to you as an eBay User and the limitations on its usage apply on that basis even though you may have registered a number of different eBay User IDs.
Never know why they don't just call these sales "up to 10% off".
Guess they think it will make you spend more.