It's done, I've left him negative feedback. Too bad the full details are only visible to me, him and the mods... but anyway I've placed it here, with no nick attached.
Day 1: Arranged with seller to meet at tanjong pagar, at 6.30 pm the next day. Made things convenient for him. Both agreed on selling price of $200.
Day 2: Got SMS from seller in the morning saying that he couldn't meet later and would reschedule the meeting for the weekend. I told seller it was no problem.
Day 2 night: Seller posted in message thread that item was sold. I thought he meant he was reserving it for me.
Day 3 morning: SMSed seller, asking for meeting time as it was the weekend already. 8 hours later, got SMS from him saying it was already sold.
1. If he decided not to sell earlier, he could have just told me and I'd have let it go. But he said he'd reschedule our meeting, and then sold it to someone else in the meantime. This smacks of dishonesty.
2. Seller did not even have the courtesy to inform me that he sold it to someone else. No word from him at all, until I SMSed him. This shows a lack of integrity.