Many of u might know this, but it's a help for those who don't. The higher the Ivs a pokemon has, the harder it will be to catch, I've tested this on the unknown dungeon (A.K,A. Ceulean Cave) and the harder it is to catch the Ditto, the better IVs it has. Therefore with that u can estimate the IVs, now...who has a really bitch to catch pokemon they haven't checked for IVs?