How do you know moldy cheese is not spoiled? This question made some people laugh, but I think it is a serious issue. There are types of cheese on which mold is cultivated, such as Rocfort cheese.

Unfortumately, some harmful mold may grow on old cheese, or one that was not treated under strict hygienic control. Most would assume the color is due to the characteristic mold, being unable to distinguish the good from the bad one.

Can I distinguish the two just based on smell color and taste?
Given the salt level, and level of "good" mold, not much can go wrong, and there is a very low risk of anything dangerous happening. It's probably going to dry out before it spoils.  Any storage that might happen is probably due to improper storage.  This is one case where smell and visual tests can help you determine spoilage. If you smell the aroma of ammonia, you probably have a problem.  If you see fuzzy mold, or mold that is off color, that is a good sign that there is some spoilage.  Any slimy cheeses should also be discarded.  Finally, if there are no obvious signs (or you see subtle signs) you can go ahead and taste it.  This is not normally something I would recommend, but again, with blue cheeses, there is a very low chance that something harmful is growing.  If it tastes off, that's not a good sign.