Fantasy trade etiquette

[Soul Daddy]

In one of my leagues I was just offered a trade. Players are insignifant, but I PM him back and accepted his offer. Since I can't access my fantasy site through work, I received this message when I returned home this evening.

"I have to wait before I will give the final say. I have another trade that is a bit better, if it passes. I will adivse..."

I have always operated under the philosophy that if I offer you something and you accept, I've lost my right to rethink things. I've also never had this happen in 10+ years. Thus, I'm pretty confused.

Is this a normal practice? How should I respond?