Less than three years ago, I purchased an LG 55" television (model 55LB6100) from Brandmart, which the black screen is now flickering off and on. Is that a common occurrence with LG televisions and is the set repairable?

Your LG 55lb6100 is near it's projected life span. That said many times these TV's last much longer. On eBay used parts for this model run from $6.00 to over $100. I used some of these on my mother's Samsung, it was easy to do and it still works fine. But you still have to figure out which parts you need. That said, unless you are really handy or need a TV for a family or bedroom, I'd just purchase a new one. The day after Thanksgiving would be a good time.

Not sure if that a common occurrence with LG tvs. TVs are so inexpensive these days you better off getting a new one.