מוכרי כסות - The רע"ב explains that they would wear the clothing to show it to potential customers; according to him the solution of the stick was to hang the clothing from a stick held up by the shoulders instead.

ובלבד שלא יתכוונו - This appears to contradict the holding in משנה ב, where wearing a garment to avoid taxes was prohibited; most explanations of that משנה are that it was coming to tell us that even though wearing שעטנז in that case was a דבר שאינו מתכוון, it was still אסור.  According to that logic, one might think that the same ruling would apply to these salesmen, however the תפארת ישראל distinguishes the tax evader as one who is getting some benefit from having donned שעטנז while he was wearing it, albeit not the usual protection from the elements, in that he avoids the tax.  However in our case the seller does not gain any benefit in the moment that he is wearing the שעטנז, and so it is permitted.   

תופרי כסות - The potential אסור here is of העלאה, as the clothing is not being worn.