Interesting thread. I've never refilled a printer cartridge, although I have considered it. (I'm cheap.) Plus, I have a feeling that my cartridge may be fade from production before I quit using my printer. The cartridges are now getting harder to find. (I can't really upgrade, since this is used with an older computer, and it's been years since any printer has worked with its operating system.)
I've found some new, sealed cartridges in thrift stores. The strangest time was when I found my first ink jet printer. (An exciting buy, since I'd been "making do" with a "near letter quality" dot matrix printer.) I grabbed it, and two aisles later, I stumbled across a new, sealed cartridge. A good thing, since the cartridge in the printer was almost empty.
Buying in a thrift shop does have the risk of age deterioration. I'm not sure how big a deal that is, but some companies provide expiration dates. I've never had a problem, and these days I don't use the ink jet printer for anything more ambitious than a personal letter or a draft to proof read.
For those with Epson printers, BE CAREFUL with refills. Epson has permanent print heads, and I've been told by owners that they can clog on off-brand ink.
And for those who do a lot of printing, you've probably heard this, but it's worth repeating--get a laser printer. They are the cheapest choice by far.
My roommate has two laser printers--one for fast drafts, and a good color model. Given the amount of printing--especially in color--those printers have probably paid for themselves with the ink-cost savings.