Mario,
The On The Dash price guide that seems outdated relies on tracking transactions that are public. And the guy who runs that site (Jeff Stein) also runs THIS forum. Lots of great advice can be found on this forum as well as at OTD. There are other sites as well. The one that has the most current update is Richard Croswaithe's (please forgive me if I spelled it wrong Richard) price guide here - http://www.heuerpriceguide.com/ which was just updated. Again, it relies on known transactions. You should poke around a bit at Jeff's and Richard's sites as well as search through this forum to gain confidence in the value of that watch.

If I had not posted about the Chronomatic Siffert I purchased this year, they'd never be able to use it to update their price guides. And I didn't tell them what I paid. Both of them were gentlemen and didn't ask.

I would suggest that if your pending purchase is a private opportunity and you decide not to take the plunge, share the info with this forum and the seller will certainly receive offers in the range of recent market prices.

Good luck with your decision!
Mike