It seems, JB, that you didn't "lose," you were outbid. This happens.
I once met an agent who brought an offer on one of my listings in a multiple-offer situation, and he sat down in front of me and my sellers, and proclaimed that, "I never lose in multiple-offer situations." He won this one, too, with an escalation clause $5000 over any competing offer.
You should know that sellers are usually - not always, but usually - inclined to go with the party with the best offer, and if you think that your agent should have talked you into offering more than asking price to start with, then; yes, it is time for you to get a new agent.
I am not going to concur that sellers are greedy and unfair when trying to pick up another 3 or 4 points on a real estate transaction, especially if they've seen values falling by more than that every recent year.
All the best,