Side by side samsung SRS536NP fridge going warm?

The man i bought it off reckons he's a technician and when it happened he said it was the thermostat freezing up, so told me to empty fridge out, turn off, leave freezer door open for 24hrs and turn it back on. This seems to wrk but after a wk or two it does it again. I have read reviews on this model on net and alot of people r having the same prob. How do i fix this or shld i just get a new fridge