Big Boy

I reluctantly need to consider selling my Rivarossi (#1254) Big Boy with tender. It is in excellent / mint condition. I would greatly appreciate advice regarding a fair price.
Many thanks

Is that a 2 rail O scale piece, or an HO model? People in this Forum are a poor choice to advise on an HO model.

My plan in your shoes would be to cruise various websites of Dealers, they are all over the Internet, and price shop typical asking prices for comparable pieces, just like you would before listing real estate. With a general idea of ballpark value, you could make an informed decision on your asking price, then decide whether you will negotiate or simply take best offer, etc.