How do you get an adult corn snake used to being handled?

Patience and perseverance. Most reptiles, though never actually becoming 'tame', will get used to being handled. If you're bothered about being bitten - wear thick gloves during the early stages of handling. Once you're confident the snake has accepted you're not going to hurt it - you can discard the gloves. A corn snakes bite is harmless (although painful) and can be treated with antiseptic.