Sometimes what happens is that your scanner does not work occasionally. You change the angle of reading, and it works for a while and then progressively gets worse. The most common cause is a dirty len. In retail, fingerprints, smudges, dirt, often glues from sticky tape, etc. are all collecting over time on the lens and progressively having an impact upon the quality of your scanning so slowing you down. The only fix is cleaning.
However, you need to be careful when cleaning as you do not want to scratch the lens. It is for this reason I do not recommend cleaning your lens regularly as you are very likely to damage a good len. As a rule clean lens as infrequently as you can.
If the scanner is working fine, stop do not clean it even if it does not look right. If you think, you should do a clean first do a visual check on the lens to see if its required.
Here is what I do if I decide to clean it.
If there are large pieces of dirt or glue mark on it. I do not want to wipe this into the lens which can cause scratching. So I try to remove it gently, often by blowing, and if I have to touch it, I use a microfiber cleaning cloth to take off as much as I can. I do not use tissues as I think they are too rough and may scratch the lens.
Next what I do is breath carefully on the lens and wipe off the steam with the microfiber cleaning cloth. Usually just a gentle circular motion with a cloth will remove most marks on a lens. If that is not enough and there are difficult marks to remove, I then use a len cleaning tissue, which are available. The ones I prefer are alcohol based as they remove fingerprints and glue without leaving streaks. Then dry with the microfiber cleaning cloth. Remember it does not need to be 100% clean, many barcode scanners will work fine at 80%.
This advice is fairly generic and should work with all barcode scanners.
A good scanner well treated should last you for many years.
