i have a chaffinch in my garden, and i can walk right up to it and it doesnt seem too bothered, it just sits there while im doing a bit a gardening or filling the feeders up, he will sit on my windowsill aswell, he's lovely.
ive noticed recently when all the other birds fly off because they've heard or seen something he wont move, he can fly and eats ok, and has no problem chasing the other males away, but im worried he's going to get eaten himself as we've had a sparrowhawk in the garden a few times recently, i no its all part of nature if he does i just want to know if he's ok?!
If he's eating and chasing other males, I doubt there's that much wrong with him. Check that there's no food around his beak which might indicate problems swallowing, and that he's not fluffed up. Other than that, he sounds like he's probably just very brave/cheeky.
A closed mouth gathers no foot.