This was the case when a German dealer secured an ivory, ebony and brass sundial from the late 16th century. It had been made by the famous Nuremberg dial-maker Hans Tucher in 1586.
Although it came with its original leather case, the compass was lacking its needle and glass, a fact reflected in the estimate of €500. In the event, the hammer fell at €6500 (£5910).
There was a similar price rise for an 8½ x11in (22 x 28cm) oil sketch Full Moon in Cloud, painted on canvas during the first half of the 19th century. There was no indication of the identity of the artist, but the provenance was documented by the inscription on the rear of the painting, which stated that the sketch was the property of Eduard Cichorius in Dresden.
He came from a wealthy merchant family in Leipzig and started collecting art in the 1850s. He was particularly attracted to works by German Romantic painters, many of whom he knew personally and several of whom painted his portrait.
In 1903, four years before his death, Cichorius donated a large part of his collection to the art museums in Dresden. Whether the collector on the phone, who invested €6000 (£5450), 12 times the guide, had an inkling about the identity of the artist or was just taken by the subject and its provenance, remains to be seen.