Bribery Primer 101
Bribe: To Dishonestly persuade someone with a gift or threat to act in one's favour...
Bribes may be Prospective, or Concurrent, or Retrospective
When the bribery done ahead of the favour expected, this is usually done to avoid easy detection. It may also be done to reduce the potential of refusal. Many upright persons are bribed prospectively and they accept it because they did not know the intent of the person bribing them. This may go on for a long time. It softens the person against a refusal of a request by the person bribing.
For example, if someone has been giving you expensive presents and paying for your foreign travel, buying things for your spouse etc. you won't be inclined to refuse them if they ask you to give them a big contract later.
Drug Lords are known to use this method a lot; they start by befriending powerful people, sometimes 10 years in advance, and they give them expensive gifts, and treat them very well for a whole decade. Then they start dealing in drugs, at that time the people in power are unable to stop them because of how much they have taken from them over the years and how much the drug lords know.
When the bribe is given just before or concurrent to the favour being requested, and is clearly designed to influence a decision in favour of the person bribing.
This is what most persons do, and this is what most petty bribes are (the type you pay to low level civil servants). This is the commonest form of bribery. It is also the one that is smallest in quantum compared to the other forms of bribery.
A concurrent bribe is usually a small amount given to unknown persons who have to exercise a discretion. The amounts could be huge, but the receivers are usually scared of being caught etc so they are usually very cautious and hide it. Some may not hide it, especially when the culture of bribery is endemic and the system doesn't punish such malfeasance.
This is when the bribe is paid long after the favour is given. This is where a person is promised (usually with guarantees) that if they act a certain way, the beneficiary will reward them in future. The persons involved have all manner of ways of securing the performance of such promises (including the use of death threats). This form of bribery is quite common with politicians and other state office holders who are aware they are being watched.
They therefore do not take their bribes when in office, but defer them till they leave office. Some may also take the bribes in false names (that makes it concurrent) but enjoy it themselves.
Retrospective bribery is common and effective. People take lands, houses in foreign nations, vehicles and all manner of expensive gifts including shares in companies etc. They engineer and arrange these bribes whist in office, but they enjoy them after they leave office.