If you normally post your parcels or letters by 1st class recorded delivery why not sent it 2nd class recorded but use postage stamps on the outside of your parcel or letter instead of the printed version the post office stick on.
I buy 1st stamps online or in books of 6 or 12. I then buy 5p stamps 2p stamps and 1p stamps in £1 amounts.
A large letter weighing upto 100 grams costs £1.18 1st class and only £1.10 2nd class. 3 x 1st class stamps and 8p in small number stamps is all it takes. I have the stamps already on the letters / parcels and the recorded delivery slip already filled in. Saves time queuing up.
The more stamps that you use the less chance the post office have of counting them and they always send them by 1st class post.
Your customer pays less or you pocket more depends on how you play it.
I send Golly badges by 2nd class delivery as an option and have passed on the saving to my buyers.
10p in your pocket for every parcel sent is a saving.