The kind of load testing you get at auto parts places is not the highest quality and is subject to a lot of variation, even with the same tester and operator. CCA testing is an iterative process, so measuring it accurately never happens outside of labs. Auto parts places use conductance testing, but that is as subject to as many uncontrolled variables as any other field test method. Carbon pile testing is probably the best. You can get such a tester at Harbor Freight for $80 before discounts.

Technically, a battery meets it's specs if it has a load equal to its CCA applied for 30 seconds and never drops below 7.2V. It can dump right down to 7.2V and stay there and it will still pass. You know your equipment will have problems there, but the battery is still "good".

Carbon pile testing consists of putting half the CCA load on the battery for 15 seconds and watching for the voltage to stay above 9.6V. Still might cause your electronics to have issues.

Add in the fact that the stores are using a piece of test equipment that is subject to damage and inaccuracy that is probably never tested and is operated by someone whose expertise is not electricity. Then multiply by the incentive to them for providing a failing test result. Now stir it all up with clamp on leads that may or may not make a good connection at the time and you end up almost as well off asking a Magic 8-Ball the condition of your battery.

One thing you didn't mention was the CCA ratings of your batteries and what outboard you are cranking. CCA directly corresponds with the voltage the battery maintains during cranking, so higher CCA will be less likely to cause issues with voltage sensitive devices.