To use the C.A.R.S. Checklist we need to have a research question in mind so that we know if information sources are on topic and worth using the checklist for, or off topic and not worth our time. For our research question let's ask, "Should the legal drinking age should be 21 or lower?"
Now let's evaluate a source together.
Let's first look for credibility in the ProCon website. In the footer they claim to be a non-profit organization. That's something we can check! If we Google search for "IRS non-profit lookup" we can use the IRS tool to find out that ProCon is registered with the IRS to receive tax-deductible charitable contributions. That's a good sign! Also in the footer there is a link to for Media & Press that lists and links to respected news sites that have cited ProCon. That's a really good sign, because people who's job it is to "run down" sources have cited ProCon. The site appears to be well maintained, and while they do have a donation button it's not the main focus of the site. ProCon doesn't appear to be an authority on the drinking age since the rest of the site deals with other issues, and an author isn't listed. Overall I would suggest that even though an author isn't listed the site is credible.
Now let's look for accuracy. The last update for this page is given at the bottom of the page. Even better the date is recent (within the last year). We'll have to read more sources to find out if ProCon agrees with other sources, but we do know that ProCon is purposefully giving both sides of the argument. Without looking at more sources we'll have to hold off on deciding whether this page is accurate or not.
Turning our attention to reasonableness the first thing we try to find is the site's point of view. We see a lot of facts, but no point of view. They provide evidence for all of the facts and arguments on the page by linking to the place they got the information. All of the arguments and evidence are about the drinking age. While ProCon is collecting donations, they aren't trying to sell a product or a position and we already know that the IRS has certified that ProCon can collect donations as a non-profit. All in all ProCon seems unbiased as they have the same number of arguments for and against changing the drinking age. So far so good for ProCon!
Finally, let's look to see if ProCon supports its arguments. They cite their sources and when we click on a footnote it takes us to a page that lists all of their sources. Looking at the list it appears to be a lot of scholarly sources with some news sources, government sources, and a few other internet sources. We can find a lot of these sources by searching for them or by using the address in ProCon's citation. ProCon's address and phone number are both listed in the footer, so we could contact them if we needed to. The address also matches the address we saw on the IRS website. So yes, ProCon definitely provides support for its facts and arguments.
Overall, since we determined that this page is credible, reasonable, and supported we can say that it's a high quality source. We'll still need to check to make sure that other information sources have the same information ProCon does to determine its accuracy, but it's off to a really good start.