Is it safe to pay deposit?

We are looking at buying an apartment near Nice and have been dealing with Conseil Patrimoine, Cannes. To hold the apartment we have been requested to pay 5% deposit into a notaire's escrow account. We would like to visit the area before committing outselves but there are only a couple of apartments left hence booking the apartment before we even visit. Is it safe to pay this money into such an account? Is this normal course of business in sale and leaseback? Is it true that if I send a letter to the notaire stating we're not proceeding that he must refund deposit within 21 days? Any comments greatly appreciated.