Me at my local dealer; " I'm looking for a used travel trailer around $10k. No more than 22 feet long and no more than 3000 lbs. At least one dedicated bed but doesnt have to be a bunk model but...
If this is electronic communication...just look online. Even most dealers in podunk have inventory listed online.
If you are in person, after they show you the first one outside your range, stop him and correct his errant ways...if he repeats the problem either leave or ask for a different salesman.
As mentioned, upselling is as old as time plus he may not have any that meet your specs, so he's got nothing to lose showing you what he does have.