How do I make sure a printer ink refill is compatible with my printer?

It's a hp deskjet 3322. I know the ones at Staples are compatible, but they are rather expensive and cost more than the printer itself. Is there a reputable place that I can just like order online and save a few bucks at least and some hassle and that will work with no problems?How do I make sure a printer ink refill is compatible with my printer?
I've used http://123inkjets.shop-desk.com with great success. They have a 1 year guarantee and free shipping making it a heck of a deal. I did look at some other places online and they ended up being more expensive so i've keep this site bookmarked for when i need refills.How do I make sure a printer ink refill is compatible with my printer?
I know Walgreen's does it. There use to be Cartridges of the world around here but there gone now...There are a few ';on-line'; places but mostly they require you to supply them with empty cartridges. The cost of shipping sometimes make it prohibitive. I know what ya mean about the cost of even refills...I have an HP F4280 and two cartridges combined (even the discount cartridges) cost more than the machine! You can get a ';kit'; to refill the cartridges yourself...but it can be messy and time consuming. Using cheap paper and printing in ';draft'; mode can help lengthen the time before refills!