Buyer Beware?

Or is it Seller Beware of today's Buyers? 

The term in real estate before all the disclosures came about years ago was Buyer Beware.  Today I wonder if it has become more of a Seller Beware market.  Sellers have the legal obligation to disclose everything about their property for sale and when in a binding contract, it is the Seller that has to put the effort and funds in to assure their property is closed and on time.  I wonder if Buyers today after putting the minimum amount of earnest money possible down to secure the contract, are still looking for a better house and a better deal!  Many times working more than one offer at a time, accepting one while they are bargaining for another without the agent or Sellers knowledge.  I believe today listing agents show protect their Sellers by requesting a minimum of 10% earnest money.  In most cases 10% would be enough of a risk of loosing their earnest money to cause Buyers to secure one contract and follow through to closing.  I have been so frustrated just this week as a Listing agent to find one Buyer attempting this trick pulling out of a contract to find Oh, I didn't get the house so I want back in this contract.  Should you as the listing agent advise your Seller to allow them back into the contract or not?  Are there any other agents that have experienced this same situation?