Assume used glasses can be purchased in shipping container lots from large thrift shop charities like Salvation Army and Goodwill.
Any storekeeper can have a few pairs of glasses to swap, but the downtown (down village ?) shop specializing in eyes and glasses might be organized this way.
Picture
large darkened room. Various Eye charts on one or both walls.
Chair, line or painted feet indicate where to stand. Tables and shelves swamped with glasses of all sorts. Maybe they are:
Short sighted to the left. Longsighted to the right. Astigmatism all around you.
A Small admission charge to pay building rent and clerk's salary.
Clerk let's in one or two people at a time. Each person can take in only one pair of glasses and leave with one pair.
They try on glasses until they find some thing better. And leave the original pair behind.
A sign reading: "If theft of glasses does not cease, patrons may be asked to strip before entering glasses chamber." is posted near the entrance. This is mostly to entertain the clerk. Another sign says: "Free eyeglass cleaning"
Clerk has random pairs of glasses for sale for those without any glasses, And for those whose glasses are in an unsalable condition. That way they have a pair to take into the swap room.
Clerk has a place to hold safe extra glasses, children and small dogs while patrons shop. Clerk has a book: "So you want to be an eye doctor" that he/she pretends to read.
Signs for the weekly meeting of the eyeglass swapping club are posted. The meeting takes place at noon under a shade tree near the shop. Several eyeglasses mechanics with their tool boxes of tiny screwdrivers attend hoping for a bit of business.