I have 2 boys that were rescue boys and weren't handled at all. Got to give credit to Hels on here because when they came to me they were a lot more social. Chaz doesn't mind being stroked in his cage but he doesn't like being picked up and being carried around terrifies him, he will nip quite hard, he doesn't like to sit still much either, he much prefers to wander around on you. Dave on the other hand will not let you stroke him in the cage, he'll come take food and beg for it but you can't touch him, he's quite scatty when being picked up as well but once he's in your arms he loves cuddles and will stretch out. I've been trying to cure Chaz for months and he is getting better but it's taking a long time. I don't think he'll ever get to the stage where he feels really safe being carried around so I try to limit that as much as possible.
The best thing in my opinion is to just take it slow. I let Chaz nip me if he's going to (sometimes I think it's just mouthing and he doesn't realise it hurts because he was never handled for the first year of his life) but when he does I say No or ouch in a high pitched voice, sometimes he pays attention, sometimes he ignores it but he's getting there slowly