Avolanche:
Follow the instructions that come with the resetter and you should be smooth sailing. Some early models malfunctioned or had premature battery failure, but most everyone seems to have no problems, especially with the re-engineered designs. As pharmacist said, the chip on the cartridge can fail too. Best to use OEM Canon cartridges for refilling.
One "quirk" is that certain aftermarket chips on cartridges are not compatible with resetters currently available. For more info see
http://www.druckerchannel.de/artikel.php?ID=2377&seite=4&t=das_zuruecksetzen_der_fremdpatronen. Use Google translate if you don't understand the chart. (
http://translate.google.com/transla..._der_fremdpatronen&sl=de&tl=en&hl=en&ie=UTF-8)
eBay has plenty of inexpensive chip resetters for sale. In general, there are red ones and blue ones. The red ones may be the first generation resetters and the blue ones may be second generation. The major differences are ease of replacing battery (s) (easier in the second generation resetters that have screwed-in bottoms), the number of batteries (one in the older model and three in the newer models), small changes in contact surfaces, and the warranty (depending on who you get the resetter from).
Instructions for use should accompany the resetter. It is quick and easy to use.
A quick check on eBay shows prices from $16.99 (free Shipping) on up. I bought the el cheapo blue one. It took about 2 weeks to be shipped from China/Hong Kong, something that wasn't advertised though now it says shipping source location. Anyhoo, it works great. A number of people here went for the resetter from Mapsy in Oregon, currently $23.55 (free ship), because she offers a 1 year warranty. I see the original chip resetter from Sudhaus is $20 (free ship). Then there are a few other knockoffs and even some more expensive AC wallwart industrial strength models if your going to do a LOT of resetting.
Lots to choose from and the ones I specifically named are probably safe bets. Whatever you end up getting, as long as it works, you will like it!