Why you can't skimp on other features of your new shopping cart, you shouldn't cut any corners when it comes to wheels. Some wheels are made out of plastic and they only move backward and forward. Others have wheels that can swivel a full 360 degrees.
The latter is preferred, as it will make it easier for you to turn tight corners and navigate difficult terrain.
The material that your wheels are made out of is also important. Plastic is inexpensive, but it doesn't have the strength and durability of metal or rubber. Plastic wheels don't navigate the bumps and impact of sidewalks quite as well.
Finally, consider the number of wheels. While some carts only have two wheels, others have four - and these are definitely preferred. Some even have stair climber wheels that will make it easier for you to get your shopping cart- either loaded or empty - up a flight or two.