If you sell via pm, that's your choice right. Seems some buyers want to stay under the radar. Not even sure why.
HWBot only provides a marketplace so enthusiasts can sell the hardware they have benched on. Warranties for clocks can never be provided, but at least the buyer has an idea what to expect.
Even if we invoke the thread only reply procedure, some pm action will still happen and you can even end the sale with: "Sold elsewhere, thanks for the space"