Do not buy microscopes from toy shops, opticians or supermarkets. It does not matter how large these shops are, chances are pretty good that they will not have microscopes of sufficient quality. Toy shops and opticians are not experts in the field of microscopy and are not retailers of scientific equipment (which microscopes are). In a catalog, I have even seen toy microscopes being sold as “research microscopes”. Evidently they did not know the difference.
Also do not buy microscopes second hand from auction sites, unless you really know what you are doing. Sometimes the seller has inherited the microscope and does not know much about it. Chances are also pretty good that you won’t be able to obtain qualified advice.