You'll get a lot of different responses to this question but here's my opinion.
I have a strict adopt not shop mentality. Animals aren't toys or breeding machines for us to exploit for our own pleasure so by not shopping for an animal means less demand. If there was an ethical standard for breeding hamsters in regards to pet shops and also for housing within the petshop then that's one thing, however it's typically very cruel and unethical.
By adopting you are providing a home for an unwanted animal which didn't ask to be brought into the world. You take it on to provide it with the best possible care, home and medical attention should it need it. You provide a safe place for said animal to live out the remained of its life naturally, with no fear.
Typically those who end up in rescues or need rehoming are because the animal is 'old' or no longer cute. Sure there are some with actual reasons like time commitments and such but some lie using that to get rid of the current older hamster in order to get a younger one. Or they simply get bored.
People are quickly drawn to the younger ones so the older ones are over looked.
You could argue that the ones in petshop didnt ask to be brought into the world and thus need a home too. But then we're back to consumer demand.
In short, myself, prefer adopting animals in general, but that's me. If you chose to get one from a pet shop that's nothing to do with anyone else. As long as you provide the best housing, care and any medical attention it'll need no one can say anything against you. Please be aware that when I say 'the best' in the statement above, know that this means the best in your area and budget as well as resources.
Don't think that just because you can't provide a 1m X 1m X 3m cage with rodipet food, 10 different substrates and loads of foraging and enrichment that youre a bad owner. As long as there's variety within the habitat you provide which differs around the world (UK 80x50cm, US 450sq" and Germany is 800sq" I believe) then it's ok
Have you got a hamster or thinking of getting on?