In my experience, barcode scanners are very much, what you pay for is what you get. When you see cheap scanners with no instructions or what so often happens, written in Chinglish (Chinese English) if something goes wrong it may be impossible to fix.
Furthermore, what happens is with obscure companies often without a website if you need a driver to make it work, you cannot get the driver. This is a major problem if the user wants to change window versions. It is best to get a well advertised brand. Even though I have seen many have trouble with these too.
You need to listen for the noise. Some scanners are just noisy. After a while the sound really gets to you. Bee, bee, bee, etc.
Then check the range they scan, too much can be a problem. You want to scan an item, and it picks up another barcode from somewhere else. What you need to do is test over the range that you intend to use them.
While doing this check how long in time it takes to read, some read very slowly.
How accurately does it need to be aimed?
Determine if the scanner can read dirty and creased barcodes. If you sell drinks, you also need to check if it can read a dripping wet can.
Now check what they can read, I would suggest as a bare minimum you need a scanner that reads 128 (widely used in warehousing), UPC (supermarkets) , ISBM (used in books) and QR codes (modern barcodes).
Look at the size of the cable, I have never heard anyone complain if the cable is too long but I have heard complaints if it's too short.
Can it take a fall? Generally, the heavy ones go crash when they fall. In most shops in continuous use, it is only a matter of time before they fall.
Lastly check if it can take moisture. I have seen plenty of scanners after coffee was dropped on them.
