I registered my pink ID on mor prom and received my covid jabs free. The Yellow book is not widely know about with Thai Institutions, the guy at the land office did not know it existed. Normally if I show it they still want my wife blue book.
Airlines use a complex algorithm for booking flights, here are some of the considerations: Shorter direct flights tend to be more expensive, day time flight more expensive. Some routes Monday and Friday are more expensive because they attract business travel, some airlines give a basic price and then offer upgrades for flexibility, seat allocation and baggage. If the flight is nearly fall the price will rise. In the case you shown I suspect its due the higher price being business.
DDP means the supplier covers all costs of delivery and tax, I have never seen any mention of it on any lazada store. They all seem only to have a nominal delivery charge, probably less than if you were to ship internally in Thailand. Hence my question.