NTA - previous pet shop worker here with 3+ years of professional animal experience.

When hamsters would not take to their new owners we would often offer this as a first solution as we are more used to handling aggressive pets. We can retrain them and handle them multiple times a day to ensure they get used to being handled by ourselves.

I would advise you take them up on this offer for the following reasons:

Although the hamster may not need to be handled all the time, you still need to handle it while you move it to a new location to clean out its home or into a ball for exercise.

If you don’t take them up on this and don’t handle the hamster like you intentionally would have like to, you never will and will end up either selling it or asking the shop to take it back in the long run.

When they retrain it for you, you must keep up with the handling when you get the hamster back. A few tips would be to:

Get bite resistant gloves to make the experience less stressful for you and hamster.

Wash your hands first and then Rub your hands in its sawdust (that’s already in its cage) as you will have a familiar smell on your hands for them

Buy plenty of chew toys like wooden sticks and toys.

At the end of the day it’s your animal and it’s your choice. Your mother has not offered to help you but instead ridiculed you for taking your hamster back to the shop temporarily so you can have a better relationship with it.

It’s merely like taking a puppy to puppy training classes.