I agree - Houdini, regardless of reason, is shy and will need a lot of time to adjust. Using treats is a great way to get them to like people. It is about creating a sense of trust, and it's easier if the bird is shy and naive around people than being preconditioned (read: abused) to be actively fearful or hating of people.
When I adopted Rosie, it was an impulse buy - but for a seemingly decent reason. When, at the store - which I will rename to "PetStupid" to protect the guilty, the so-called "handler" told me of a number of things they did to catch the bird -- chasing it around with their hands, cornering it... right then I knew things were very wrong. They had also put in a webcam at night because the bird would just sit there all day, but metallic objects would keep vanishing. Rosie collected metal things, and - at night when nobody was in the store - she would do somersaults as entertainment.
After the clerk told me of what they did, I decided the bird had to be taken out of there.When I got to the cashier, she (who still worked there 2 years later) told me of the same things, especially the hand-grabbing.
As a result, Rosie was constantly terrified.
However,
After six months, she started to do somersaults for me - solely to get my attention and laugh. As I laughed, she would do more. That was a good sign.
After a YEAR, Rosie felt comfy enough to take millet treat from my hand.
After almost two years, she would say "I love you".
She often does run and hide in her happy hut, but can be just as brave at other times.
At times, she will reluctantly acquiesce and perch on my finger, and I will sometimes scritch her neck in the bathroom (an isolated environment). Not for too long because I can tell when her anxiety builds up (when she starts chirping in a yelping tone, that means it's time to put her back). And I know it's not due to me personally, but that she is scarred for life. She is up to 10 minutes of being out of her cage and allowing me to let her perch (and occasionally scratch her neck), but it's been slow going and due to how the PetStupid people treated her, there is no way she can be fully adjusted. Not ever.
But her somersaults and "I love you" - I know she understands... and the somersaulting to me whereas she would only do that in the store when nobody was around, I know she has a slight bond and in her own unique way. And maybe that's why Rosie tolerates me at all. I understand her, and can relate in some ways...
As a result, I howdied* Scooter, a green check who is roughly 3 1/2 years older - they (amazingly) get along, so they cohabitate. Rosie still does her somersaults, Scooter still readily hangs out with me, and they get along and preen each other (since I know Rosie prefers Scooter scritching her neck).
* howdying; a process where multiple birds are introduced, slowly, via having them see each other from their cages, and later given time outside together. If any aggression is noted, they would be separated but Rosie and Scooter bonded fairly quickly, with Scooter (the shy one) needing more time, but it worked out amicably.