Too many people have asked me about the slender 3 and why I exited the market only to re-enter a few years later. Here's my story between 2003 and 2011. Collecting coins was always a hobby of mine. But only in 2003, after moving to Cardiff, did I take it seriously. I used to buy silver and gold coins in bulk from scrap traders and jewelers only to separate the half decent coins and sell the rest on as scrap. This way I began to build a decent collection by only paying slightly over bullion value for coins. Slowly by 2004 I started to buy non bullion coins as well. Within a year I acquired a few very rare pennies, including an UNC 1903 open 3; and became more interested in pennies. In those days the demand for pennies was stratospheric (I am of the opinion that the market for coins is subdued at the mo). On ebay you had people like C Morgan, Tony C, L Bamford, M Platt, C Davies, G Schindler, F Fiona etc who'd snap anything of interest and the selling price for pennies in auction-houses wwas pretty steep too. If you recall in 2003 a decent sovereign was selling for £45 - 60, yet at the same time a cleaned 1875 H specimen penny from the Adams sale was going for about £960 (https://spink.com/lot-description.aspx?id=3011262). I still retain this coin (The same coin will perhaps sell for around £1500 today but a sov is selling for around £200). So I decided to sell my pennies and invest in silver. By 2009 a mate and I had about 300 kgs in silver and we started a refining business in Birmingham producing 990 silver for big names to put their stamp on. By 2012 the metals market nosedived and I exited the business after taking a 30% cut on my investment. However rather than taking my share as cash, I took just over 90 kgs in pre 1920s silver. Again I sold all the 1911-9 coins and damaged coins for scrap and I still retain over 30 kgs of at least clear date pre 1911 silver, which have not been checked for variants. I have stocked this in an bank vault and I intend to use this for my retirement project. Must be fun sorting through each coin using an ESC book, some of which are from the mid 1600s. Since 2013 I have returned to pennies and have started rebuilding.
Coming to your other question 19k was pretty good but considering the demand at that time I'd say it wasn't unexpected. I had a cash offer of 13k for the slender 3 and 5k for my 1903 open 3. I gave the coin to LCA on the condition that I would take 13k+ (after commission) or not pay the commission if the coin did not sell. The die number 5 penny, which sold a year prior, went for more than the slender 3. The pattern 1933 sold for over 30k during the same time. The market then was very buoyant. In my opinion (adjusted for inflation) collectibles' prices are low at the moment. Property is on the up (but I believe it might have peaked) and this is precisely why I created a tread called markets in the "everything goes" section