Well for me I never used any tricks. I had one betta refusing to eat for a good two weeks - but he was sick to begin with. Another ate after a week, one the same day, another a few days after. Spartan ate rigt away, Admiral ate 2 weeks later, Colors ate 1 week after, Madame ate right away, Voldemort hasn't eaten in two days, Rose finally ate a little, Marge ate right away, Tina ate a day after, and Zebra ate right away.
I think it depends on the betta o.O I usually let them wait it out until they are hungry and decide they want to eat.