As pudusku said and since I HAVE A LEXMARK AND KNOW...
THEY CAN INDEED BE REFILLED UNLESS
The ink has dried out inside of the cartridge-even partially dried will clog it up and render it unsuitable
IF there is damage to the print head
You can follow a couple different avenues here!
If there is no problem with your cartridge and the clerk was just trying to get you to buy a cartridge (happen ONCE to me!) follow the directions at this link and it'll show you and tell you how to go about it all! BUT MUST BE TRULY ABLE TO BE REFILLED! SEE BELOW!!!
I'm NOT coordinated enough to refill mine so instead I send mine to a company.You visit their online site,PAY online for the refill -price is usually $13-14 PER CARTRIDGE depending on how many you need filled,size, and type-ie black or color.They'll send you out a "JETPAK MAILER KIT". (a mailer envelope)You put your cartridge in it,mail it back to them, and they'll send you back a cartridge with ink in it-black or color depending on what you sent to them.They'll handle any problem with the cartridges!Here's one I've used before:
PLEASE READ REGARDING THEIR INSPECTION:
Every cartridge will wear out sooner or later, often due to one of the many resistors in the head failing. Before a cartridge is mailed back to you, your cartridge will be tested for print quality. If it does not pass the test, your cartridge will be discarded and you will be sent another Jetpak (or, if you're a frequent customer, just a certificate that allows you to include an extra cartridge in the next Jetpak you send in) at no additional charge.
IF YOUR CARTRIDGE FAILS THEN I'D GET AN OLD USED ONE FROM A FRIEND,FAMILY,ANYONE(!) and return it to them.It takes a while so don't expect it to be returned FAST,UNLESS you send it OVERNITE delivery.(Could STILL take a week even at that method of S&H)
These even have a piece written titled "What You Should Expect From Your Recycled Inkjet Cartridge"!
Hope this helps!God bless you and yours!