@williethejolitz,
The info below is what I do using my computer, not the app. Do remember that seller's listing titles can skew the results because they omit information, in titles and item specifics.
Last October ebay made sweeping changes to searches in many categories including model trains. I started a basic search from an ebay page, for "HO scale Santa Fe and a drop down list appeared, with Locomotives added and also the model trains category pre-filled.
On the page that opened there were 2,900 results. but by using the filters in the left hand column, the results could be pared down considerably. Selecting "Brass" cut the results to 344 items. Other filters such as Diesel locomotive or Steam Locomotive also lowered the number of results.
Since the changes, I've found starting searches with the Scale HO, O, N, etc. Then adding a road name, and loco type (HO Scale Santa Fe Diesel/ Steam locomotive) gets a better return of relevant results, than adding scale later in a search title. Then I use the various filters in the left hand column to pare them down.
"THERE IS NO SUCH THING AS FOOLPROOF, BECAUSE FOOLS ARE SO DARNED INGENIOUS!" (unknown)