No. The Addendum for Sale of Other Property by Buyer doesn’t require the buyer to provide evidence to support her decision to waive this contingency. The only requirements in the addendum are that the buyer notify the seller in writing within the time stated and deposit the additional earnest money with the escrow agent in a timely manner.
Buyers should consider the risks of waiving this contingency when they don’t already have the proceeds from the sale of another property. A buyer would be in default on her contractual obligations if she waives the contingency and then fails to close solely because she didn’t receive the sale proceeds.