Tip a Real Estate Agent?

[Joseph Schommer]

Hi BP!  

I have been working with a RE agent for the last 6 months trying to put an off market-deal that I found together.  We got to the point of contracts being agreed to and we signed, but just before seller signed he pulled out!!!  It's a little mysterious as to why but that's not my question.  My question is:
Is it appropriate to tip my RE agent?  If so how much?  Gift box-thank you?  

She's done so much work on this and has created an easy and painless process for us not to mention the contracts she's drawn up etc.  What's an appropriate way to show gratitude for the work her team did on my behalf?

Thanks for everything you do!