Very soon (I hope) I’ll be selling my trailer —waiting on the manufacturer to give me a delivery date for the new one --I will sell mine immediately and list it for $8K OBO --the dealer has offered me 6K for it in trade in --clearly the 6K is firm and anything above that will be going into my pocket (or toward the purchase price of the new trailer). So the OBO may be “personal choice” —right now one of the stable workers is trying to get her parents to make an offer --I would take 6K from them immediately —because the stable girl has been a hard worker, every day for two years. I like giving a kid like that a break. Once I have a firm delivery date --and someone puts 8K in my hand --everything ends. However, assume that the manufacturer’s delivery date gets close, and I’ve had no offers --well, at that time, your best offer of $7K looks a lot better than the trade in offer. Or you make an appointment, show up on time, are polite, explain that $7K is the best you can do, it’s a great trailer --hey, I like you and the trailer is yours. Show up late, point out everything wrong with the trailer, sigh a lot, act like I’m a jerk for asking $7K --nope, I’d keep it rather than sell it to you.
As the others said, make the offer. Worst that can happen is the seller says no. If someone is offended, remind yourself it is business. Maybe the “nice guy” who gets mine for less isn’t really a nice guy --just acts like one --doesn’t matter --I’d still rather sell to someone who acts nice and appreciative of the care I’ve put into my trailer than someone who acts like a jerk.