Never get too involved. Know your boundaries.

Unless you plan to become your client's new webmaster, database manager, programmer, graphic designer and towel guy combined, draw your boundaries. Never get too involved. For instance; don't do any programming. Make it clear from the start that your client needs to do the programming in-house and that you will not code a single line of PHP or ASP.

You're giving the customer advice and is transferring knowledge to his company. Period. When you're selling SEO, don't use words like "key ready" or anything like that.