I've heard that it can be difficult to even get permission to dig a well, even if you can afford the price tag.

Unless you have permission from them, you probably won't hear anything from the lender. 

It’s common as people adding pets without permission. 

What type of permits/permission I would need to acquire from the city etc.

The way I understand the situation is this: If the Seller signs and gives the Buyer written permission to market and sell the property than you can.But: I do not buy or sell properties on the MLS.I would love to see what others with whom use the MLS have to say.

In our area, we are not allowed to give out codes without seller permission, and in no circumstances do we allow buyer's access to our MLS keys. 

I will add get permission to back some cookies... nice cookie smell is comforting.. also bottles of water with your name on them.. lender there to do instant prequal is nice as well.. you can't do this but when its your listing.. you can offer a free cruise certificate.  

Second to that, our website explains it in detail (I can't give that out here without permission though).  

The bank would rather get some money then no money so you can actually (with the permission of the owner) negotiate with the bank as well.

I have an out of state owner that would like to give me written permission to see one of his homes.