Hi-end coffee machines are a micro-market, and coffeesnobs buyers make up a micro-part of that market, so your results will also vary on time of year, phase of moon, etc.
Having said that, a 2 year old Giotto should go for at least $1800 - $2000 (IMHO), given new price has come down lately to around $2600 I think. (Ignore the occasional excellent deal that some recent Giotto owners got!). Ignore the requests for selling it at 30% new - that is silly!
Coffeesnobbers like to know a bit more about their potential machines - when was it last serviced? How often did you backflush with water / chemicals? Have you always used a good scale-inhibiting water filter? Has the OPV been set?
You could also list a few more manufacturers details that make it different from an older ECM Giotto - new control board, pressurestat, etc.
Edit your original for sale post so buyers dont have to scroll through the conversation to get answers, and even lay it out with bullets / highlighting, etc.
Finally, comment every month or two to keep it near the top of the "for sale" list. It may be that your buyer isnt here now, but will be next month.
hope that helps, and good luck with the sale! (my fee is 10% :D )