I assume all collectors have paid too much for some coins but also got some good buys below market value. In 2003 I got my first VRBS ROMA/she-wolf twins chi-rho type. I thought they were rare. I now have six of these and know they are not rare. In 2003 I was in a bidding war with someone else on ebay for this coin. The coin is ex Jean Elsen, 1998, then ebay from Tom Wood, chi-rhocoins. The final price I paid with shipping was $343. Attached is my coin, another from CNG sold for $75 and one sold on ebay Dionysos last Monday for about $115. Mine is nice but I'll never get my full amount back. I'm a wiser buyer now. Hopefully in my collection there are enough good buys to counter the high prices I sometimes paid for others. ;D
I am frequently amazed at bidding wars for coins that are not actually that rare. I saw the example that sold Monday, but it was already bid up over $100, so I was not interested, though the price was not excessive. I could not have listed it for much more. Of course, coins with religious symbolism have a greater appeal. Below are four examples that I have sold recently, all for $100 or less-- from top to bottom 100, 85, 75 and 65.
Yes, I paid far too much. I've never paid three times the normal worth for any other coin. But I've gone up to 50% more for something that I really wanted. On ebay I often put a coin that I don't want in my watch list just to see how high it goes. I also check prices on CNG, Wildwinds, etc. I used to check prices on acsearch.info but now you have to pay for premium membership to see them. For recent auctions I check the past sales on sixbid and numisbids.
I have to admit that I have also paid far too much for a couple of coins. In one or two cases it was to fill a very specific gap. But these days I am much better though. Every now and then one slips through. But I usually feel better once it is in hand :) One weakness I still have is to sometimes overpay a bit for lower quality coins simply because they fill a spot. Usually a better quality one comes along soon and then I regret it.