If you have a look at
his feedback, the same slipper clutch (not necessarily the same item) was sold earlier but they buyer complained that he "only sent half the bits" which I guess means the matching clutch plates?
If you look at the pics, it also appears to be missing the springs and spring caps too - how much else internally is missing?
There was also a thread a while back about the "only one track day" use statement, which (if I remember correctly) someone found out that it was actually from a race bike? I think it was KJ that also pointed out the wear that could just be seen on the basket too...
If you're thinking of buying, I would get as much information as possible from the seller. Drop him an email and ask about the springs, caps and internals. Ask for more photos. Ask what is exactly meant by "one track day" and which bike this came from (as this may lead him on to tell you where it came from). It's better to be safe than sorry...