1. Discount season: For example, in the summer discount season from July to August, Christmas, New Year's Day, Mother's Day or various large-scale national festivals, general shopping malls will give discounts. At this time, the cheapest price of L 'Oré al is in chain stores such as Watsons or Boots, and the price is lower than that of duty-free shops. For example, I bought a red anti-aging facial cleanser with a discounted price of 99 baht. The original price was 159 baht. Sometimes duty-free shops sell 199 baht, but the price of this facial cleanser in domestic counters is more than 100 (currently RMB exchange 1:5). You can see how different it is.
2. Non-discount season: the price of airport duty-free shops is slightly lower or similar to that of the local area, but not necessarily. I have time to go downtown and see that L 'Oré al has a red label sale. I won it decisively, and the price is definitely lower than that of the airport duty-free shop!
I have verified it many times, and I speak from experience.