Vacant land across from Walmart

[Scott Ruffrage]

I have a .6AC lot across from Wal-Mart for sale. There are two other land owners involved with a total of 4 AC's for sale.  I'm asking $200,000. for my lot. Publix and Wal-green have submitted offers in the past but back out. They were both using a third party developer for the purchase.  They have both returned to the table. My question is this. What is a standard amount to ask for earnest $, or a non-refundable deposit. In the past they got a 6 mo. due diligence, with a 3 - mo. extension clause. 

Thank you

Scott R.