What a load of fuss and outrage over nothing.
The bod needed a bulb, so he bought one for £15, not the fiver he could have found one for. Net loss £10, except it's not a pure loss as he has his bulb and it works. By his own admission, he'd rather cough up than say "No" then and there and wait to buy one later. The bulb will probably last about 8000 miles; work out what ten quid is over pence per mile, it will make you feel happier.
All this 'It's a rip off, bloody dealers' from fellows who quite happily spunk pounds and pounds on bling to personalise their bike, as it will 'Say something about them'. Yup, the dealer maximised their profit on a bloody 2p bulb. Why? Because they could, right at that moment of most pressing customer need. The same way that punters can spend hours upon hours haggling down the cost of their new motorbike to zero... Or just kicking tyres, sucking their teeth over the rip-off of it all.
Worse things will happen in the world today. Get over it.