• Numerical with Dollar Sign: $12.00
• Numerical without Dollar Sign or Decimals: 12
• Written: twelve dollars
The researchers expected that the written/scripted prices would perform best, but they found that "the guests with the simple numeral prices spent significantly more than the other two groups."
Therefore the trick to selling stuff is get people to forget they're spending money.
Image source: Flickr member cuttlefish under Creative Commons