Yes, those are the fans I was talking about. They move the air from the cabinet through the evaporator coil to give up heat. Once the coil starts to freeze and slows the airflow, the problem gets worse. Like Gartywood said, you need CLEAN coils so the air flowing through them can transfer heat, so the condenser coil also needs to be clean and it's probably easier to get to on this unit. Vacuum off any dirt blanket and wet-clean the coil. Pros use an acid-based coil cleaner, but you may get by at home with detergent / water sprayed through the coil & rinsed well - a garden type sprayer will work. Some coils may look clean, but you can still flush an amazing amount of crud out sometimes. I worked on a walk-in cooler the other day that had the same problem and cleaning the condenser resolved it. You can shine a bright light through from one side of the coil while looking at the other and see the air passages.....
It's hard to tell from the pics, but the evaporator box looks a little rough. Beverage coolers have a drain in the bottom of the evap pan so water condensed out of the air can drain out - usually via a vinyl tube to a pan in the compressor area. Since floral coolers provide a high humidity environment, I'm not sure how they deal with this. Maybe they have a deep pan and some water is retained? Did you see any kind of a drain tube leaving the evaporator housing? Also, check for holes in the housing which may have corroded through and are allowing air from outside of the cabinet in / out.
If all of that checks out, then it could be a TXV that is malfunctioning or had been mal-adjusted or it could be a low charge issue. When the unit is running, the tube entering the top of the CONDENSER coil from the compressor should be hot - probably too hot to leave your finger on for more the several seconds. The ends tubes should gradually get cooler as you feel the from the top to the bottom indicating the the condenser and its fan are removing heat. A low charge will be cooler at the top of the condenser. I see there is a liquid receiver on this unit also, so it probably holds more than a few ounces of refrigerant.
Another look from a different refrigeration tech may be in order & I don't see why it would matter whether it's a residence or biz if you can pay for a service call. A make & model number would help a lot - there may be a tag somewhere on the compressor deck which may ID the type of refrigerant, amp draw, etc. if you can't find anything on the cabinet itself.
Good luck!!