We manufacture skins, not cases. Many people underestimate the importance of the skin, but in fact, it is the only product that will preserve your phone's look and keep it away from wear & tear signs that will lower its resell value in future. Cases are also fantastic and very good in protecting from drops, but they will scratch your phone because dust and dirt will be allowed. So always start with skin and then, if you want, put a case on top of it. It's like cosmetics - you begin with a serum and then finish moisturisers for the best results.

The price you are selling your phone for depends on its condition, and there are three types:

Mint (this should be your target): your phone is fully functional with no significant damage. Your phone does not have scratches on the housing or screen if you had EasySkin installed from day one until the day you decide to sell with/without a case. For Mint condition phones, you may only lose 20% or less for one year if you decide to sell. 

Good: your phone is fully functional with no significant damage. Your phone may have some light wear and tear. For example, when you used only a case without EasySkin under it. For Good condition phones, you may lose 40% for one year if you decide to sell. 

Poor: your phone is fully functional with no significant damage, but it may have major wear and tear such as scuffs, dents and deep scratches - you do not like either cases or skins. For Poor condition phones, you may lose more than 50% for one year if you decide to sell. 

If you buy cheap skins from untrusthorty sellers - yes, it might. But if you buy from a reputable brand then it will not just not leave any sticky residue, but it will literally preserve the condition of the phone as it wss on the moment of application. The materials matter, that's why EasySkinz uses only custom-made 3M materials, special repositioning adhesive techology that gurantees the skin will never leave residue even if left for years.