I don’t think the difference of strategy is linked to the nationality of the auctioneers, but to the category of them.
I would say that one can mainly distinguish two different categories of auctioneers one particular strategy for each of them.
1. Horse dealers stables or stud-book.
They are picking horses among their own stock or the stock of their members.
2. Pure auctions companies (like Fences)
They are selecting horses among open group of horses without considering to own the horses or to sort through their members horses. The unique aim of theses auctioneers if to bring the best possible quality to the buyers.