Imagine, you search for your dream dress on a sales site only to find out that it was listed and someone else bought it just yesterday! What a let down! You might be tempted to send a message off to that person asking if they will sell the item to you for more than they paid, after all, if it had been an auction, a higher bid would have won, right? Or you could even message the seller a higher offer; maybe they haven’t shipped it out yet!
Don’t do either of these things; it’s incredibly rude. The person who bought the item wouldn’t have bought it if they didn’t want it. Offering them more than they paid would mean they make a profit, sure, but they bought them item to wear 99.9% of the time, not to resell. It also makes a lot of people very uncomfortable.
Messaging the seller is asking them to break a sort of contract they have with the buyer. Not only is it rude to the buyer, it puts the seller at risk of being called a scammer and getting a bad review, and it puts you at risk of being called out for rude behavior.
Maybe it’s not a recent sale though, maybe you see it in someone’s wardrobe post, or see a photo of someone wearing it. You might be tempted to message them something like “If you ever think of selling….”. It’s best not to do this. Most of the time, the person isn’t selling the item. Asking someone to sell you something they like and enjoy can trigger a strong feeling of possessiveness; it can feel like you are trying to take away something they own and like. It also puts an emotional burden on that person; they are forced to either tell you no, sell you the item now, or remember until the end of time that if they sell the item, they promised they would track you down and tell you. It also can feel a little stalkerish. It’s best to just wait and see if the person lists the item for sale, or to make a want to buy post instead.
In short, if you want to buy something owned by someone else, don’t ask them, beg them or bother them about it. Just make a want to buy post instead.