There are often questions about what exactly Return Best Price is in the lead system and how it fits into ping post; return Best Price is quite literal in this case. When a vendor includes the parameter Return_Best_Price=1 AND you have the source setting configured, the system will consist of a price in the response. What that price is and how it is calculated will vary. Return Best Price is just the technical requirement needed to pass price information between buyers and sellers.
Vendors can optionally use "Return_Best_Price" parameter in their requests if it is enabled in the source settings. Usually when vendor sends the "ping" to the lead system, they get a simple response without price information, like this:
<?xml version="1.0" encoding="utf-8"?>
<response>
<status>Matched</status>
<lead_id>3658</lead_id>
</response>
In this case, the lead price is internally determined (somehow), and the lead cost is taken from the source settings. In other words, the lead cost is a firm amount set in the source. The lead cost is what the vendor is paid for the lead. When they use "Return_Best_Price=1", then the system takes the best price after the margin and returns it to the vendor in the response like this:
<?xml version="1.0" encoding="utf-8"?>
<response>
<status>Matched</status>
<lead_id>3657</lead_id>
<price>22.5</price>
</response>
Please note that the "price" in the response, in this context, is used as the lead cost in the lead system. It is because "the best price for the vendor" means what the lead system pays the vendor for the lead, which is the lead cost from the lead system's point of view. In our example above, the lead price that the partner pays is $25, and the margin was set as $2.50, so the price minus the margin is $22.50. This is set as the lead cost, the amount the vendor gets for the lead.
Lead price: $25
Margin: $2.50
Lead cost: $22.50
In this case, the lead cost is not a firm amount, but it is dynamically calculated based on the top bid and margin settings. We call this "dynamic cost." So, when the vendor uses the parameter "Return_Best_Price=1", the system returns the highest amount as an offer to the vendor. The vendor can decide if they send the "post" part of the lead based on the request from the lead system (if they consider the amount they receive for the lead appropriate).
If the vendor sends the "post" part, the lead is sold exclusively to the highest bidder. Now, if the source is set as Allow Using "Return_Best_Price" Parameter in PingPost API, yes, but sold non-exclusively. Then the system tries to sell to all possible buyers, not only the highest bidder. That way, the lead system can maximize the profit because it would not sell the lead to only one buyer but to all possible buyers, if any.