Just find related subs to your service you are selling and post some comments, be creative, there is a huge traffic on reddit. Post link of your shop but don't make it look like a spam or ad, you can use more accounts to reply to your own comment saying it works. But you have to be creative and make it look believable and not like a scam. Also try to get some older reddit accounts, if they have good karma it's even better but it's not necessary.
For example, when I was selling Spotify accounts last year I found with Google a random subreddit related to Spotify and I made a comment about how I brought account really cheap on some random shop and it's still working after a few months, and I put link of my own shoppy than with second account I replied later with something like "Lol dude thanks, I actually brought account and it's working" and I instantly started getting a lot of customers. This is just an example, you can come up with your own better idea.
I'm not selling account for months now so I'm out of shape
wait that's actually a fucking genius idea, have never even think near that XD
thanks pepelove