BCG, You are getting as sound advice as you can for not having done even the barest field research.

lol I will only hope to add some tweeks you may want to consider.
Have enough change “available” as recommended to not be the one that has to take a little nip if it gets to that. If they stand hard on the $11.00 purchase, you don’t want to take the $10.00 because you don’t have the four singles.
Be ready to state “I don’t have a lot of change. Why don’t you take two more and make it an even $5 instead of $4?”

or “I’ll give you one more at $?? (1/2 off) and we can make it an even $10.” or “Take both of those and you can have everything for $??.”
Take Fzzy’s advice on signs to heart. LOTS of signs! Put them up far enough ahead for drivers to have time to think about it. Never mind making them try to read and remember an address. Just “BIG GARAGE SALE- ½ Mile Ahead!, 10 Blocks Ahead!, NEXT RIGHT! Then a BIG arrow or balloons at the corner of your street or drive. Make them on Day-Glow or bright colored paper, then paste that to cardboard. (cheaper than colored poster board) Keep them looking hand made and not something from a commercial operation. [you may ponder putting a typewriter size note on the bottom of each sign saying “This sign is displayed for a garage sale at ????? Lake Dr. and will be taken down by ??:?? o’clock”, to show responsible intent and avoid a resident that may have to clean up similar unretrieved trash from making your day short]
You may want too make a point to be sure each customer hears a “HI!

Look around at everything.” They are going to do it anyway, just make them and their wallets feel welcome.
(Just a thought)

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