I"m sorry that I have to tell you this, but it's already been done. Even here in Milwaukee Wisconsin (as opposed to Milwaukie Oregon, bet you didn't know that I knew there was a Milwaukie in Oregon, I'd also bet you don't care ) there is or was a guy who would do personal fittings and help with bike selections and purchases at their homes, I think he had a van with advertising on the side, I believe he mostly dealt with the upper end of the market and as such only marketed to higher dollar customers (a market that I am on the opposite demographic end of) . I don't know how successfull he was or even if he is still in that business, but I suspect not.

As noted, try to get a bunch of used bikes and start up a craigslist business selling them in the evenings and weekends, tack on a $40 fee for your personalized services and see how it goes. But I'd suspect you'll average two to eight hours of time with each customer, and will have the usual frustrations of dealing with returns and folks wanting a guarantee and a refund if they later decide they don't like cycling, or if they decide that they wanted something different because their use and needs and conditioning changed.

You're idea is kind of like a personal shopper coupled with a consultant advisor. Good luck. I'll suggest you align yourself with a health club or a personal trainer in your area to help connect you with people, go for the cross-over customer.