I wish to remind you that you must be the first to say 'thank you' everytime you purchase something, especially food. Don't wait for the seller to say 'thank you'. Never expect him/her to be the first to say thank you just because you are paying for the goods/service.
You should rightfully thank him/her for the efforts and time spent to prepare the food or whatever service that you are getting. Do not place value on your dollar notes. Your heart must be able to see who the real giver is. Be sure to see who is the 'real provider' of your food when you transact. When your heart becomes sensitive you will see the He who is behind he/she you are dealing with. Then you will quickly without hesitation or delay, say thank you not only with your tongue but with your inner most heart. If you do that you can be sure that you don't belong with those whom the Prophet had referred to when he said: "Those who are not thankful to the people, they are not grateful to Allah."
But you O son, you must not only be thankful to people and be grateful to Allah, you must witness who is the source of benefits and acknowledge immediately by being the first to say 'thank you'.