A real collector will rarely sell a work unless he can replace it with something even greater that has more personal meaning.

And if there are no new specialists tomorrow, to whom will today's advanced collectors sell their rarities?

And in these precarious economic times, it wasn't easy to persuade collectors to sell unless they had to.

Such a development must seem remarkable to anyone who watched this market in 1984, when collectors were selling, not buying, Tiffany.

In June 2011 a private collector sold it at Christie's for a sum of £67,250/$109,080/€75,656.

The smart collectors buy the cars on their 16th or 18th birthdays and sell after they hit 20.

Now collectors are buying and selling more discreetly through dealers.

"My father wanted it in the 1970s and couldn't get it because at the time the collector wouldn't sell it."

They provide a secondary market that permits collectors and others to sell wine outside normal commercial channels.

Some collectors may sell rare baseball cards over the internet and very often on eBay.