In the UK, the parties to a contract of sale will often agree on a price some time before completion of the purchase.
A deposit is usually paid by way of security for this purpose and sometimes monies are also paid in advance, e.g. for building insurance or tenancy deposits. These monies may be particularly important to one side or the other if a contract were to break down. It is not uncommon for a purchaser to lose a deposit on a property sale in UK if they have failed to complete on time - even where there are no damages or losses suffered by the vendor, who may be unaware that they ever had this money in the first place.