I think it is just right to give you a negative feedback.

I texted the seller at 9am today; we then agreed to meet at 1pm for the item. And so I made so much effort just to arrive to our meeting place at 1pm because I hate being late. And at 1pm, i texted the seller that I am already in the meeting place. He (or she, rather) suddenly replied that she forgot our deal because there was an emergency.

The seller should have informed me about it. If I did not text him/her, I wouldn't have known he/she wouldn't come. Effort, time and money were wasted. VERY UNPROFESSIONAL! Think twice or thrice before you make a deal with this seller.