That also is my understanding. When you buy it, it’s MS. When you try to sell it, the dealer says AU.
A left-handed pitcher's slider should break down and away from left-handed hitters, and down and in on right-handed hitters. A right-handed pitcher's slider should break down and away from right-handed hitters, and down and in on left-handed hitters.
Slider originally referred to a raw coin that was uncirculated, but got some wear sliding across the table, from its storage cabinet. In TPG parlance, it is a coin that on any day could “slide” in grade from high AU to low grade MS.