In my custom woodworking business, I let folks (who want to) come to the
lumberyard with me to select the stock to be used for their project. I
charge a flat rate for the time spent getting the lumber (same as my normal
labour rate), and let the customer pay the bill at the yard (They get my
contractors discount).

This lets the customer be involved in stock selection, but also lets me be
there to point out things that they may have missed because they don't look
at wood every day.
Some things that I've found:
1) many customers are amazed that you have to buy more wood than you are
actually going to use - the concept of waste is often something they haven't
dealt with before.
2) every customer I've ever dealt with this way is *amazed* at the cost of
cabinet grade lumber.
3) after picking through a pile of stock, most customers start to realize
that there is a lot more to selecting quality lumber than just getting
pieces that are the right size. Those little knotholes, color variations,
grain irregularities, surface dings and checks that they don't see (or
assume can just be "sanded out") help them realize that part of what they
are paying for is the fact that I can look at a few $100+ pieces of wood,
and see which ones will work, and which ones won't.
4) when the customer watches me piece together what parts will come from
which board (and write it down in my shop log), they start to realize that I
can (usually) get a lot more out of a board than they can. They also realize
that there are a *lot* of little pieces in furniture that they never thought
of.....

Over all, I usually encourage a customer to participate in this phase of a
job. By keeping them involved, they start to realize that they really are
getting a lot for what they are paying. This is also a great place to realy
fine tune what the customer wants. When they see a bin full of curly maple
next to a bin full of birdseye, (next to walnut, cherry, mahogany, etc) its
really easy to tell who has realy made their mind up about what they
want.... I've had more than one customer decide to postpone a project while
they reconsider what type of wood to use....

its worth noting that the work I do is high end custom furtniture. This
wouldn't work for many home renovation type contractors.....

--JD