How much does everybody's buy rates vary from day to day. Mine can flucuate around ~0-100% a day which seems like a lot but has to be normal. Usually the range varies about 30% but it is common to sell twice as much on a given weekday than the previous day for no apparent reason.
What are your buy rates mine usually are in the 3-6% range
I calculate this by total unique visitors divided by # of sales
I think the term used a lot is sales conversion rate or something similar...
Ours is pretty consistent as long as we're getting regular traffic. Because of our free pair of shoes contest we sometimes get listed in a newsletter or website for contests and we get a lot of traffic that doesn't convert into sales (just people wanting free stuff).
However, most of the time our sales conversion is pretty consistent... our conversion rates right now are around 2-4% of unique visitors. We also get quite a few phoned in orders that aren't calculated into this though, so the number's probably right up there with yours.