Just like household fridges, when they stink, they stink. The odor actually imbeds into the plastic liner and insulation behind it. The baking soda/water is a start. You may never get to odor completely out, but this will help. Then leave an open container in the fridge. Use essential oil.
Recipe:
pint jar
2 cps baking soda
20-30 (or more if needed) drops essential oils - vanilla, orange, lemon. Best with citrus or vanilla.
Leave jar open in fridge and periodically stir it to give it a burst of fresh scent.
If you want use some to wipe down the walls.