Galaxy Websites
It all comes down to, how many errors are you willing to accept?
What are the chances of chosing a web developer that knows the standards?
Less than 1% of people that call themselves web developers produce validated pages. That means there is a 99% chance that you will choose someone that will not develop your website to the standards, but you will be paying for that loss for as long as those pages are online. That is why I say, "how many errors are you willing to accept?" I produce 100% error-free validated websites using the W3C.org validation service (the group that issues the web standards). The few web developers that validate their work get to display this symbol on a page that has passed validation:
You should be able to click on the symbol to verify that the page validates.
Your website should look great and it should be coded to the standards set by the Web Consortium (the standards people), but less than one percent of websites ever reach that level. How do you get to that level? Hire someone that produces and has produced all their websites to the same high-quality standards. The standards published by the Web Consortium (W3C.org) are the guidelines to follow in order to achieve that level.
It turns out that some websites will put this symbol on a page to make you think it is validated, even when it does not. It is possible that the page validated at some point in the past, then some updates were made that broke the code, and could be in the process of being fixed, but that depends on how long the symbol remains without the page being fixed again. Most I have encountered go on for years without being corrected. It is the responsibility of the developer to check the page periodically to insure against that happening. If the symbol remains on the page for longer than a few days, be suspicious of the developer.
I use several tools that go through every page on a website to ensure I didn't miss anything. After all, I am human like all the other developers. The one difference is that I care enough to check often so that you don't end up with a page that has errors for years on end.