Yes, the sales tax would be a deduction as Cost of Goods Sold if it is product you later sold to a customer. Or, if you keep and report inventory on your taxes, it could be included in your inventory amounts.
Also, the entire amount received by your customer (including sales tax) is included as income. So, if the total the customer paid was $21.56 cents (for example) that is income to you. Your expense deduction would be the amount you actually paid. I believe you pay a discounted amount for MaryKay but the charge the full sales tax.
If you purchased product for your own personal use, that is not deductible. So, you would subtract it out from your total purchases. Only subtract your actual cost you paid plus your taxes not the retail prices.
If you purchased demo products, you can include them as Advertising or Supplies.
