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Taking empty cartridges to a store is the surest way to get something back aside from a sense of satisfaction. If you print and buy frequently, this is the way to go. Most office supply stores will accept spent cartridges as part of a rewards program, so you'll want to find a place that you visit frequently. Local participation may vary. Office Depot accepts ink cartridges as part of their rewards program. Staples accepts cartridges purchased from them and will provide a $2 rewards credit. Often these programs reward with discounts on more ink. Keep returning them to keep saving money!
Determine your best option. Find the right store. Keep the cycle going.