The wider picture
Often, I'm asked to refer the reader of the sales letter to the client's website. What they see there can have an enormous effect on their purchase decision.
If your sales letter looks professional but your website doesn't, it instantly puts doubt into their mind. Is this a professional company we want to do business with? Can we trust them?
Also, if you're referring prospects to a certain part of your website (for example if you want them to sign up for a newsletter) then it's important to make that section obvious for when they visit the site. If they have to spend ages trawling through your site to find a link, you risk losing more potential customers.
Who's talking to your prospects - and what are they saying?
I always include a contact phone number at the end of a sales letter, so how you respond to prospect's phone calls is crucial, too.
If your call handling staff aren't clued up on the offer you've been promoting in your sales letter, or if they sound less than professional, you could lose valuable sales.
I tell it as it is!
When writing a sales letter, I always take these and other peripheral elements into account. I'll ask to see your website and offer my opinion - beware, I can be very honest. As a client said to me the other day: "I like working with you as you have great brutal honesty, which I respect".
But it's so important for me that, when you're paying for a sales letter, you don't just get great sales copy but that all the other elements work together to push up the response.
In return, you're welcome to tell me what you think of my website! (Which, incidentally, I designed myself in case you're wondering.)