I don't want this to come off as mean in any way so I hesitated even saying - but the typical buyer for a jacket like this is a different type of buyer than a St. Johns buyer. The typical St Johns buyer doesn't want attention pointed to the item being vintage, etc., most of the time even though they are aware its not current. There are a set group of designs that have been made and they know them all and the color absolutely has to match their other pieces (no fading, etc) and it has to look new. They can be an upscale buyer in some ways and 99 out of 100 times are buying to wear and swear by St John. For some reason I have heard before of stories from other sellers where things were worn once and returned like it was Saks or something and not a private seller. As far as the vintage Sears buyer - they usually know exactly what they are looking at, know its more scarce and are happy to have it. But there is enough variation in items where they aren't going to always find the exact same thing twice Ditto the really old Levis and older work clothes. I have held my breath waiting to see what a buyer thought after they pay good money for something that isn't perfect and they are delighted where you may hear more about a catch in a St Johns
Now I am not saying to not sell St Johns because there is a market for it that can be competitively bid, etc. Unfortunately you just dealt with one bad apple, or at least was unrealistic in the type of service they expected. I wouldn't let that one person stop you from selling because you can't please everyone no matter how backwards you bend.
I would buy/bid on this jacket in an absolute heartbeat if it fit my favorite guy as he has more modern versions of this. I probably won't be able to afford it at this time, but I'd be interested in watching the auction or checking out the listing once its up and you decide where its going.
I would say if i was the person putting it up for sale - i'd try it more towards august where you have folks thinking about winter and fall more - but if its on your website it can go any time. I find that vintage Sears stuff tends to stay in the USA as far as buyers, with the occasional Japan or Norway/sweden - not as popular with australian buyers but that is just me - someone may sell all of their sears stuff to australians so its hard to say.