I agree with your assessment that a garage sale immediately before an extended vacation would not be high on many people's to "to do" list. As for garage salers and garage sale customers..... They come in two general flavors:I am no garage sale expert, but Friday wouldn’t seem an ideal day to some? And with such a short time before the Sunday (I think) vacation trip. Seems odd why that day was chosen to start, Friday and Saturday. (Saturday and Sunday are typically used by many.) And if heading on an extended vacation, a two day garage sale would not be high on my list before departure.
Customers: A. Casual shoppers looking for deals on things they personally use B. Pro / semi pro "pickers" looking to purchase things for resale.
Salers: A. Casual Salers looking to unload excess stuff B. Pro / semi pro salers catering to "pickers".
Its not unusual for "B" customers to start on Friday as a way to beat the maddening crowds on Saturday. Likewise, "B" type sellers with pickers in mind will often start on Friday and hope to sell out by Saturday.
The victim appears to have been an "A". But.... if she was selling say, high grade cosplay gear, she might have been functioning as a "B" and started on Friday, hoping to get the high dollar cosplay stuff sold- then close early on Saturday.