body: I once heard that there is a certain level of reasonable expectation that is guaranteed by law when it comes to making multiple deals with others.
  
  
  For instance, is the following legal or illegal to do.
  
  
  * Bill offered to Mow Janes lawn for $1, which is agreeable.
  * Bill mows the lawn, and gives Jane a bill for $1.
  * Jane happily pays.
  * A week pasts, and Jane asks Bill to mow her lawn again.
  * Bill mows the lawn again, and give Jane a bill for $2
  * Jane asks why $2 and not $1, like last week
  * Bill says that he changed the price within the last week due to high demand of his services, and that is what he charges everyone now.
  
  
  I do not mind which country the law exists, or if it exists at all; I was told that this was illegal to do (anecdotally), and I just want to get a quick opinion (not used in any legal way, just to cure my curiosity) and see if they were telling the truth or not.
  
  
  Thanks!
  
  
  
title: Multiple deals in a row and reasonable expectation