The first thing we learned is that size is very important. The length of your child's inseam is much more important than his or her age. The size of a bike is measured by the diameter of the wheel but the frame can vary from bike to bike so it's important for your child to try it on for size. We knew we had the right bike when our guy straddled over the bar flat-footed and he had a two-finger clearance to his inseam. For more tips check out here and here.
When we got home, the first thing we did was give it a good scrubbing. It was important to us that this new 'gently used' purchase didn't feel less "shiny" to him. Next we added a new bell. And then a new bike pack on the handle bars to hold snacks and trinkets. Finally we added stickers to the frame to really customize it. It's not the prettiest thing in the world. But it's his and he's proud of it.
The final purchase that really sweetened the deal for him, was the addition of a Trail-Gator Bicycle Tow Bar. This bar attaches his new bike, to the back of his daddy's which turns them both into a clever tandem bike. Perfect for reducing fatigue-induced, roadside whining. I see long bike excursions for the whole family in our future.
In the meantime, here are my etsy finds:
• Going To See My Baby Lavender Bike Screenprint by Strawberry Luna ($25)
• Vivienne Riding Her Bike Print by Matte Art ($35)
• Happy Bike Couple Pair of Table Lamps by Czech Pub ($70)
• B is for Bike 2 Canvases by Bubba and Boo ($100)
• I Heart My Bike Reproduction Fine art Print by Michele Maule ($20)
• Bikes Print by Leah Duncan ($12)
Before & After: Emily Henderson Transforms a Senior's Studio Space
Monica & Austin's Charming Bungalow
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
Ercol Bar Stool
How To Cook Fluffy, Tasty Quinoa
True Greek Recipe: Paximadi Bread Salad with Tomatoes, Feta and Capers
neat!
when i couldn't afford a new bike for my daughter, i cleaned up her brother's old one and together we got some sparkly stickers and some streamers to customize and girlifiy her new ride. she was happy as could be.
Great idea, jsev! It's great to hear about parents reusing and recycling toys by going to second-hand stores, Jackie. That's exactly what we need to be doing right now.
If it's hard for your kiddo to part with things they've become attached to, you can get some helpful hints in this article:
http://tandemteaching.com/how-to-avoid-toy-overload-a-teachers-secret-unveiled/
I hope it's helpful!
I own that original of Michelle Maule's bike art and love it! We're big bike nerds in my house, so it's on our bike art wall. :) I've got my Gocco prints of bikes on maps on that wall, too -- as well as in my little shop of craftgasm!