Nope that does not work.
I have a theory for the Chest (V4 only, not sure about V3)
When you buy, if it is ___, it will:
1st in shop: Transform to temporary baby
2nd in shop: Give gotchi points
3rd in shop: Give present
4th in shop: Transform to temporary oldie
This has been tested, and I hope it helps you next time you spot a Chest in your V4's shop.
I always get a present or gotchi points.
I'm not being mean but all tamagotchis are different and yours just might have gone in that order.
Did you test it 3 times to make sure?
If you didn't try again 3 times and then do and see what happens.
So really that is not true.
Sorry I just don't believe your 'theory' because its most likely not true.