It depends on what it is....Lilly Pulitzer I always crosslist in modern even if its vintage, ditto 80s coach bags,, and in fact people would more likely look for those in modern.
I have noticed though if the item is more of a wardrobe staple, or its shoes, things with BIN's and store inventory does much better. When I am looking for modern clothing I am usually "on a mission" to find something in particular. And I do believe, that unlike buyers who are "collecting", modern shoppers are doing mostly the same thing. Unless it is the item or brand of the moment, or is higher end designer stuff I would probably BIN it.
If you are listing vintage in modern, I think that like was said before, unless its a prom gown, and sometimes even then...I would definitely have a BIN option. There is a lot out there and sometimes the one where the person can buy it right away instead of timing for an auction ending a week later, wins out even if the other item is right on the money and the BIN "will do".
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Deborah...Gloria Sachs is not a big keyword draw by itself, and your item is priced much higher than other GS stuff by comparison. (rightfully so, though!). I might ditch her name in the title and go with:
Designer White Linen Ribbon Applique Cardigan Jacket M 38
If it fits.
And what about quoting the label resource to note that she was a textile designer? It may help "romance" the item for the potential buyer
http://www.vintagefashionguild.org/labels.php?labelno=475&mode=search
I might put a just slightly higher BIN on it too but just above the opening bid.