Any day you can trade a Glock for a Sig is a Good Day.Most Sig owners want nothing to do with Glocks on trade.Sigs are a work of art when it comes to guns.Sig is one of if not the best gun out of the box you can buy.Remember you get what you pay for.I would take the deal all day long.Then I would trade the 23 for a P229 or M11A1.Glocks are good guns but Sigs are better.If you have to make changes to get the Glock to shoot like the Sig why not just buy the Sig.You should try it out then make up your mind.
Something I've learned over the years is that those 'once in a lifetime' deals come along about once a week. Whether that's firearms, motorcycles, cars, jewelry & watches, real estate, or anything else.
I just shrug it off and think "Wasn't the right thing for me, at the time. There'll be another opportunity coming along soon". Long as ya keep your eyes and ears open.
If it just didn't 'feel' quite right (nothing nefarious, just that 'feeling'), then it's usually better to listen to that 'little bird on your shoulder'.