1. Club A is interested in a player
2. Club A asks Club B for permission to speak to the player
3a. If Club B accepts, the player and his representatives speak with Club A to see if they can verbally agree on personal terms. If they do, skip to 4.3b. If Club B don't accept, then it's down to Club A to try and convince them that a deal would be worth their while (or if the player himself states his desire to move/hands in a transfer request) otherwise the interest usually ends here. Anything that Club A does at this point which directly involves the player or their representatives without acceptance from Club B could be considered 'tapping up'.4. If the player & Club A agree personal terms, Club A will then open talks over the sale with Club B until they come to an agreement. If they do, the player is sold. If not, see 3b.
This is my general understanding?
1 - Buyer is interested in a player and sounds out the player's representatives / agent about the likelihood of them wanting to come and what terms would be required to make a deal.
3 - Buyer may also sound out the player's club about a move but will not be too bothered about being given permission as it is merely an "informal" chat with the players representation at this stage.
4 - A transfer may be agreed between clubs but it will certainly be after terms have been sorted "informally" with the players representation. No club wants to risk a public formal bid to be then blown out by the player involved.
5 - If no transfer is agreed then it makes little difference and the player's representation may "advise" them to make things difficult at their club. The selling club will likely not make any formal complaint about tapping up as they will
6 - Eventually a deal gets done, or a new contract gets sorted, or the deal gets kicked down the road to the next window or whenever the selling club can get their ducks in order. And everybody agrees that tapping up rules have never been adhered to since the inception of footballers contracts and they're really rather silly and antiquated.