Selling to small firms is easy, because it's usually clear who makes the decisions. In most cases, it's the CEO, perhaps with some inputs from an accountant or the team techie.

Selling to a huge firm is another beastie entirely–especially if what you're selling will change the way they do business. The power to make decisions is often dispersed among multiple people and groups, and it takes time, effort and patience to work through the (often) byzantine politics.

Fortunately, corporate behemoths tend to behave in a predictable pattern when buying from vendors, according to Mark Sellers author of book The Funnel Principle (and one of the smartest sales trainers around, in my humble opinion). And that buying process provides a structure for your sales activities: You react to their buying process by actually helping that process along.

Here are the six stages, with what you must do at each stage:

1. The customer recognizes that a problem exists. The prospect's firm is not going to buy anything unless they perceive that they have a problem that needs solving. Note that a problem can also be an opportunity; the inability to address that opportunity represents the problem that needs solving.

Your job at this stage: You'll be working with your initial contact, and perhaps one or two decision makers, to clarify the details of the problem.

2. The customer define the economic consequences of that problem. The prospect's firm can't possibly make an intelligent decision on whether the problem is worthy of attention until they have an idea of how much the problem is costing them. Without a dollar figure attached to it, a problem is just a wish list.

Your job at this stage: You'll be working with your initial contact, and perhaps one or two decision makers, to generate these estimates.

3. The customer tentatively commits funding to fix the problem. If the customer recognizes that there is a problem and that the problem has economic consequences (stages 1 and 2 above), then they'll have to decide if taking the next logical step of committing funding to solve the problem is worth the effort. They may not know the exact amount, but they're willing to put down, in writing, a number that represents an intent to spend.

Your job at this stage: You'll be presenting your findings about the problem to large groups and speaking one-on-one with decision makers to build consensus that there is a problem and positioning your solution as the most likely way to fix it.

4. The customer defines the criteria that will determine the final decision. It is only after the customer has gone through all three stages above that they begin to define how to fix the problem. Previously, they may have had an idea of what's needed (e.g., we need CRM because we're losing customers to the tune of $10 million a year)–but they haven't determined how they'll decide which system to buy.

Your job at this stage: You'll be working with the customer on some document, such as a Request for Proposal (RFP), that defines the problem officially and states how they expect the problem to be fixed.

5. The customer evaluates alternatives. This is when the customer looks at the available solutions and decides how they will fit with the budget that has been set to fix the problem. Note: If there is no firm commitment on the four previous stages, a sale is probably not going to take place.

Your job at this stage: Continue to present and meet with decision makers to build momentum and to fend off any possible competition.

6. The customer selects a vendor (i.e., you). It is at this point that the real decision is made, based on the commitments made at all five prior stages. Needless to say, if you've worked closely with the customer on the previous five stages, you are almost guaranteed to win the final business because you've helped to "frame" the problem, the budget, and the criteria.

Your job at this stage: Close the deal and work through the final negotiations.

Sounds easy, eh? Well, it get easier the more you do it.

By the way, the above is adapted from my recently published book How to Say It: Business to Business Selling. (That's the link to the Kindle edition, since I've gotten a much of emails asking whether the book had been Kindle-ized.)