The Honest Truth is that Validation is Pure Bunk
The Honest Truth is that if somebody comments that your Web site is a coding nightmare. And, asks: Is it any wonder that you are having problems? They are nothing but a SEO scam artist trying to take advantage of your naivety.
Another tip off is when they tell you that:
“[Your Web site] is based upon pre-1999 design practices which means it is eight years out-of-date.”
I have been there, and have had that happen to me on numerous occasions.
First of all, the need for W3C Validation is total nonsense on many different levels. Validation has some benefits, such as a way of fixing display bugs. But, in no way does sloppy coding prevent your site from ranking well in the SERPs. Google has said so itself.
Every Web site has a display design. Some designs are in fact horribly bad from a SEO point of view. But, a good SEO Web site design no matter how old it may or may not be certainly wont prevent your site from ruling the SERPs.
All of the advice of any SEO who offers these types of comments should be called into question.
For the honest truth is that they are just trolls trying to scam you into spending your time making worthless busywork changes to your Web site. Or, worst yet trying to scam you into purchasing their expensive SEO services.