Hi David, I am a brand new paying NGC member as of today - so you are probably ahead of me on this. I see the NGC cert tool lists the value of the 'rosie' dime at $565.00 and the mercury at $75.00. I do have many years experience with eBay and, most specifically with coin auctions the past 3 years. I have seen the star designated coins go for very close or more than cert value b/c there are likely collectors looking to fill a hole & willing to pay the premium. I collect mostly Franklin Half Dollars ('beines' / 'beiners' / 'beautie Bennie F's'!) and I know I could expect to sell any (non-star) general pop. date (MS or PF) at 60% of the cert value in a best case scenario. Likewise I am usually able to pick any up on eBay auction for 50-70% less than cert. value fairly easily. So those are the tools and parameters I would use if I were to consider selling a coin from my collection. Hope this helps, cheers.
~ Brother Lance