Not knowing which particular state you're referring to, it is difficult to know the precise wording of your state's tax law. While it is possible that such a tax holiday is in effect, it is likely that out of state sellers may not have been aware of a short term tax holiday of just a weekend.
Currently here in Florida there is a limited sales tax holiday on specific items. Of course, since Florida hasn't enacted a marketplace facilitator law, eBay doesn't collect sales tax for this state. While merchants that sell the specific items exempt from tax for this limited time which is primarily back to school items should know of the tax holiday, they may not have been able to set their listings to not charge the tax if the listing duration is longer than the tax holiday. In that case, I would advise the seller to refund the amount of tax collected on eligible sales during the period to the customer.
Of course, out of state sellers, may not be aware of the tax holiday although if they were required to collect Florida sales tax, they should have received a bulletin.
As I said, not knowing the particular state, I can't really offer much useful advice. However, I would probably advise you to check with your state's department of revenue regarding getting the overpaid tax money refunded.
"It is an intelligent man that is aware of his own ignorance."
