Sounds like "Deal-Making 101." The Buyer wanted the home. The Agent was trying to help the Buyer get the home. The comment is misplaced because the Agent can't predict how the property will appraise, but it doesn't sound like the comment is unethical. It sounds like the Agent worked the deal to help the Buyer win the house.
As for putting in a complaint to the Local Board of Realtors about the Agent's conduct, I'd say this: prioritize what you as the Buyer are trying to accomplish. If your goal is to buy a home, and you are truly that upset with the accepted price, then get yourself out of this deal and move on. If you have suffered some material "harm" such as expenses incurred, you need to consider that, too.
Do you want to get into a messy dispute with the Realtor over a misplaced comment? Or do you want to buy a home?
But since the house did appraise, then the Buyer has purchased the home at market price. The other bidders were below market.
I'm curious to know just how much higher the bid is above what the Buyer "really" wanted to pay. With interest rates so low, the payment might literally be a couple of dollars more than the imagined "ideal" price in the Buyer's mind. In which case, if the Buyer is "in it to win it" and become a homeowner, this whole discussion is moot. The Buyer got the house; end of discussion. Deal Made. Deal-Making 101.