In King Pin (1996) during the first scenes, we see the protagonist having trouble with his car, so he takes it to a mechanic.

The mechanic wastes no time spotting the problem. He even dips his finger in the fuel (from the fuel pump or another part of the engine that had fuel) and put it into the mouth of the protagonist for him to taste the sugar.

It is later reveled that Bill Murray's character poured a bag of sugar down the fuel tank.

The question is: How did the mechanic reach to the conclusion of sugar begin added to the fuel? If it was sand, it could have been possible to detect because unlike sugar, sand does not dissolve into liquid. Sugar does.

Was it a common tactic for sabotagers to mix sugar with feul?

In King Pin (1996), during the first scenes we see the protagonist having trouble with his car, so he takes it to a mechanic.

The mechanic wastes no time spotting the problem. He even dips his finger in the fuel (from the fuel pump or another part of the engine that had fuel) and puts it into the mouth of the protagonist for him to taste the sugar.

It is later revealed that Bill Murray's character poured a bag of sugar into the fuel tank.

The question is: How did the mechanic reach the conclusion that sugar was added to the fuel? If it was sand, it could have been possible to detect because, unlike sugar, sand does not dissolve into liquid.

Was it a common tactic for saboteurs to mix sugar with fuel?