When visiting another part of the world, you should always consider the affect tourism is having on the locals. Often tourism is a good thing for many areas as it will bring in money. But this is only the case if the tourists are respectful, otherwise you may find that the local community has to spend more on cleaning up the streets and policing during their busy periods than what they have actually bought in.
If possible, it is nice to try and use some of the local shops for your shopping instead of the chain supermarkets. Supporting local businesses will allow them to grow and be there for years to come. Some smaller shops simply cannot compete with the larger chain stores and often miss out, but if we all visited them and purchased something every time we went away, it may just be enough to keep them afloat.