Let's see.....

Did the tech print a self test page directly from the printer? If he did, and the line was still appearing on the page, the problem is with the printer itself and not whoever is doing the printing.

Did you try a different toner cartridge? If not, borrow one for a couple of minutes from another printer that uses the same cartridge and run a test print. If line still appears, then the problem is inside the printer.

If the problem is inside the printer, chances are it doesn't have to be replaced. A competent hardware tech should be able to diagnose the problem and just replace parts.

Maybe the printer just needs a good cleaning on the inside.

If the steps above were taken, the next likely suspects would be the fuser assembly and possibly the transfer roller assembly. They are replaceable parts.

It sounds like you need a good hardware tech. Many companies only have software techs in house.