I think as a retailer it's something you have to do as it only costs you time, in the same way gift shops wrap things for free if their small and independent.
What you should do though is make sure you get *something* in return. For example, do you have a shop mailing list to send out emails? They can be very useful, especially if you sell on-line or are planning to, but also so you can contact people when you have offers on. People who get the bike shop to pump up their tyres are probably the ideal people to be able to email about your special offer on a pre-winter service (in October when it's a bit quiet in the workshop - not that I know that it is, but for example) And it's always good to be able to email known customers when you order in a box of widgets and then realise that you already have a box of widgets but it was hidden behind the wotsits
So, when you pump up their tyres, have a visitors book on the counter, and say something like "It's £x to pump up tyres normally, but it's free if you're on our mailing list - we just email you about special offers in the shop" - I bet 95% will sign up.
I'd recommend mailchimp (free) for maintaining a customer mailing list, btw.