Real World Advice Requested

Coming from a university compsci program, I know a lot of theory and have played around with my linux box for a few years, but have little practical business experience. I'm wondering how people running small businesses in the real world decide on what solution to use for their clients. How can they be sure they're selecting something that other professionals would choose? Here's an example (sorry it's so long):

For instance, someone's come to me and asked me how to handle their invoicing and data tracking for a local shipping and delivery company. Currently they have a couple of employees in their office, who are not very computer-literate. They type up individual invoices in Word, each on a separate page, and that's pretty much how they keep most of their records of what they shipped, client name, cost, hours, location, truck #, etc. It was OK at one point, but they've grown fast and now have many orders per day (we're talking big items - $1000+ per order, a few trucks).
I could make a custom database program in Access. I could tell them to get a cheap linux server on a PII or something, build a small intranet, and use MySQL and a PHP application that I write. I could introduce them to Excel and keep their data in there, just using a template for invoices. I could find a commercial package that might kind of work. I'm sure there are lots of other ways to do it.

How do you guys in the real world decide on a solution? Which solutions should NOT be used in a real-world business? When do you decide "Hey, I don't know enough about this to trust myself with their business, I should tell them to get someone else or learn a lot more first". I'm sure if everyone did that, there wouldn't be many companies around.

Anyone got any advice?

One of the most important things to do is give them options. Not too many, that can scare them into doing nothing... afraid of making the wrong decision.

You have to ask them questions. What are their growth projections? Will they want now, or in the future, the capability of providing extranet access to their customers?

I'd provide them with a cost quote for a simple Access solution and a simple intranet PHP/MySQL solution. Explain the benefits and drawbacks of each.

Just remember that they do not want to learn your business (computers) and they know their business, so offer them something easy, stable, manageable.
Don't try to make a business out of being cheaper, but point out value in your solutions.
I personally would go for something browser based, or Access based, to leverage simplicity, reuse of the existing skills and value for money.
Don't forget to sell some reporting tools and printing capabilities!