I would say that they are not "untrained." Also you could say that IDing a favored enemy would be "within your field of study," but it would be limited to the very narrow check of "is this one of my favored enemies or not" with a simple yes or no answer. To get more info, like do Rakshasas have Damage Reduction, would require points in the specific knowledge skill, for the example above KN(planes).
on the second question, if you search something he didn't want you to, he should just tell you see nothing. Or that you find what was actually there. I'm actually kind of confused as to what you are even asking here.
A ranger may make Knowledge skill checks untrained when attempting to identify these creatures.
This means a ranger can make the knowledge checks to identify a favored animal without ranks in the requisite knowledge skill. He can still fail the check - but there is no limit to the DC that he can reach. Essentially that text says that for the purpose of identifying creatures, a ranger treats knowledge skills as untrained skills (like climb and swim).
I thought I should also mention that a ranger does not need to identify a favored enemy to be able to gain his favored enemy bonus against them. However, identifying creatures (which the ranger gets bonuses for if they are favored enemies) allows the ranger to identify special offensive and defensive abilities that may help him in combat.
This is similar to the smite evil class feature: it'll work against evil enemies even if the paladin doesn't know that they are evil, and even if the enemies use some spell or ability to make them not detect as evil.
Common people are pretty poor compared to adventurers. Normal skilled professionals (soldiers, merchants, etc.) live off something like 10 gold per month. Thus, your GM could easily tell you you find "nothing of value". If he wants to give you something useful you could find mundane stuff, like rope, rations, 10-foot poles, etc. Maybe a masterwork artisan's tool if he's feeling generous.Okay. What if it's a store or the rich side of town? (Especially at lower levels)
A rich store isn't going to be easy to break into. This isn't real life, this is Pathfinder. Any merchant looking to stay in business is going to have invested in some type of security.
When I run, most stores that have anything of value to adventures (magic shops, Armor/Weapons, ect) have a myriad of tricks in store for would be thieves. The smaller shops usually employ a couple of henchmen 24/7 as security.
In the age of magic there is no reason why a low level adventurer should be able to kick down the door and loot the entire players handbook.
Okay. What if it's a store or the rich side of town? (Especially at lower levels)
You are heroes- not thugs or burglars. My Response is “You find nothing of value”.
I also say that Ranger can ID their favored foe on sight, but in order to know more than that they need to make a check.
Well the shopkeeper could have a gaurd dog for his shop. that would then bark and town gaurds start coming I don't think a low level character could take out the whole town gaurd. It also works as a pet.