jeff chimed in before me. if I were in your shoes, I would have probably leaned on Craigslist and the area subreddit (the latter is very hit or miss, but I could see something niche like records doing really well.) I'm not a vinyl guy, but I'm sure there are a TON of niche forums out there worth looking at as well.
I really wish you could apply multi-armed bandit approaches to physical problems like these more easily; obviously its hard to do A/B testing when you only have one actual supply.
Yeah, I actually only recently started to understand the impact that area subreddits can have - great channel for certain audiences. My intuition is that most of my target audience for vinyl isn't yet on Reddit, but maybe that's changed and I just haven't realized it yet.
There are certainly a lot of forums out there too, but most of them aren't local to one area, so most of the sales are online (I did a lot of business through these forums in the past).
In retrospect, it would have been rad to run this as a fully fledged A/B test. I honestly just didn't know that the ads would have quite the impact that they did.
I really wish you could apply multi-armed bandit approaches to physical problems like these more easily; obviously its hard to do A/B testing when you only have one actual supply.