Maximum 4-5 good quality stickers will be sufficient. There is no use of providing 10-12 or even more stickers(like an another forum supplies) as half of them are either thrown away or keep lying in cupboard for years. IN OTHER WORDS: We actually pay for only 4-5 or maybe 6 stickers but get 10-12 of them!!
So select only 4-5 stickers which are liked by most of the people and then supply them. This will help these ways:
Low wastage of stickers.
Comparatively lower price for a set.
Cut the number to 4-5 and increase the quality and decrease the price by just 15-20%, this will help get better profits as well as buyers will be more satisfied getting better quality and at a lower price.
One more suggestion:
Select 10 stickers of different styling and post their pics on the forum(stuck on cars) and then make it mandatory to buy at least 5 at one time and buyer will be free to select any 5 of the 10. For the custom selection, since work load will be higher, so the price can be higher(around 66-75% of the price of a set of 10 stickers) but this will also again help by reducing sticker wastage as well as better quality at a comparatively lower overall price.