why do people sell empty cartridges on ebay?

[nightowl]

i was just on there trying to find a cheapo cartridge for my lexmark and there are LOTS of used empty cartridges for sale. why?

(prob such an obvious answer i know)

you can refill them, some places will pay for old ones as they then refill and sell them on cheaper than a brand new one.

Our school collects them and makes a little money selling them on for re filling.