My Craigslist ad for buying junk US silver is still working well. I bought about $30 face value the last couple of days at 25 times face, which was about 3 times face below spot price.
My ad reads:
Buying Junk US 90% Silver Coins - $25
Will pay 25 times face value for 1964 and older 90% silver US coins.
Have $500 cash to spend at the moment. Offer ends when cash runs out.
Call anytime: 555 555 5555
I use www.coinflation.com/coins/silver_coin_calculator.html to determine current value per dollar face value by calculating value of four Washington quarters. Then I subtract three dollars or so and make that my offer price.
When I placed my last ad, coinage was worth $28 or so per dollar face, so I set my price at $25. I now also post how much I am looking to spend at the moment to keep people with much larger quantities from calling. Sometimes people want to sell me $1000 face value, if you can believe it. I just don't have that much cash laying around.
Next time I do it, I am going to try $4 or $5 below actual face value and see if I get any hits.