The worst for this panhandling is the Heathrow Express sales tout at Heathrow Terminal 5, who is allowed to work inside the secure area, in the corridor leading from baggage claim, and who forcefully tries to sell the grossly overpriced tickets on the train service to Paddington, without any mention of the Underground service just outside the arrival area.
I asked them what was the best way to Knightsbridge, and was told "Heathrow Express to Paddington and then either the Underground or a taxi". The fact that there is a direct Underground service from the Terminal 5 station that departs more frequently, takes less time, doesn't involve nearly as much walking along the way, is direct rather than with connections, and costs 10% of all this mullarkey (because a First Class ticket on the HEx was what was offered first - for a 15 minute journey) was completely ignored.