Announced capacity and actual capacity

After 750 copies saving mode for simple text with ink up to 20%, the toner level warning light came on. I pulled out and moved the cartridge, but not change, so I will reach perhaps 800 pages ... which is not the 1,500 pages advertised by the manufacturer.
Note that I am a computer, I print in the office most of the time, and I do not think I buy Samsung toner today sold at a higher price than the printer, so ...