How much earnest money to put down on a p&s agreement?

[Daniel Pitta]

(Wholesaling question)

When crafting a purchase & sale agreement with the seller, how much of an EM deposit is customary to put down in order to tie the property up so you can flip it to the end buyer? Also, if you're unable to find a buyer during a 30-day period, how do you approach the situation with the seller that has already agreed to sell you their property? Thanks in advance.