Do you do a SOS search before financing equipment purchased at auction? What about consignment auctions (Farm Bureau, FFA are examples) do we need to know the seller and do a search?

You might check with your legal counsel on this issue. We do not do UCC searches on sellers, whether outright purchase or during a consighment auction. From RA9:

9-320 - BUYER OF GOODS

(a) Buyer in ordinary course of business. Except as otherwise provided in subsection (e) of this section, a buyer in ordinary course of business, other than a person buying farm products from a person engaged in farming operations, takes free of a security interest created by the buyer’s seller, even if the security interest is perfected and the buyer knows of its existence.

Do you think farm product excludes farm equipment?

I do think farm products excludes equipment. If you look at the definitions in Revised Article 9 you would see the following:

Section 9-102

DEFINITIONS AND INDEX OF DEFINITIONS

(a) Article 9 definitions. In this article:

(33) "Equipment" means goods other than inventory, farm products, or consumer goods.

(34) "Farm products" means goods, other than standing timber, with respect to which the debtor is engaged in a farming operation and which are:

(A) crops grown, growing, or to be grown, including:

(i) crops produced on trees, vines, and bushes; and
(ii) aquatic goods produced in aquacultural operations;

(B) livestock, born or unborn, including aquatic goods produced in aquacultural operations;

(C) supplies used or produced in a farming operation; or

(D) products of crops or livestock in their unmanufactured states.