You never know when you will need to transfer something heavy from one place to another. It is always better to be prepared than risk back injuries. Though there are a lot of shops from where you can buy sack trucks, there are always the same factors that you should look for to suit your needs.
You should always consider the amount of weight that the folding sack truck can carry. Will you consistently need to transfer 100kg of weight from one place to another? Or do you just need one that can carry just the right amount of weight? To further serve you better for your needs, you should also consider the durability of the materials used.
The durability of the materials defines how long folding sack trucks would hold. Even though you wouldn't use it frequently, low durability materials will only lead to wasted money. The most important part of the sack truck is the foot plate. You should make sure that the footplate is made of heavy duty metal to accommodate the weight you will put on it since you don't know when you might need to replace tires, or bring coolers as big as refrigerators from one place to another. Aside from the foot plate, the wheels should be able to handle rough terrain.
It will always be a plus when the sack truck can be easily stored at the back of your car. The sack truck should be foldable to accommodate the constraints in the space available at the trunk of your car. It would also be good if the folding sack trucks can easily be hung at the rear side of your car or placed on storage grills at the top of your car.