You can probably use a magnet on the frame to check.
My Sig 1911 and my Dan Wesson Valor both have a duty coat that covers the frame and slide. Both are steel/stainless steel.
Sometimes you can see a definite difference in the texture of a steel versus alloy frame but it is not always easily detected.
When I bought my Sig 1911, I looked at the gun and asked the LGS if the frame was steel or alloy and they did not know.
We found a small magnet and it stuck to the frame. I bought it on the spot.
I much prefer steel over alloy.
http://www.discountgunsales.com/sig-...1-pr-5061.html
I found this gun with a little help from Google. You may be disappointed.
I have not checked the Sig web site. They may have more information on that particular gun.
http://sigsauer.com/CatalogProductDe...ss-nitron.aspx
I Googled the Sig web page and found THIS!
I would snatch that up in a heartbeat. Sig DOES build a P220 in stainless and with a Nitron coat.
If that is what the shop has and it was not beat up, I would whip out my CC in a New York minute.
HTH