As you might know, CoolMart comes a feature of showing more than 1 product thumbnails in the category browse page.
But there is small patch that should be applied to Virtuemart Core file in order to achieve this. Don't worry, this is not a Core Hack, it is extremely innocent change.
This patch comes with the QuickStart Package already, but in case, you perform a Virtuemart Update (through VM Admin panel) or you install the CoolMart One-By One method, this patch will be missing.
So you should do it manually. Don't forget!! Every time you update your virtuemart to a newer version, you need to apply this patch manually each time. Otherwise, only 1 product picture will be visible in the category browse page.
Look at the 117th line and find this line: (it is on 117th line in VM2.6, it might be located in different lines depends on your current VM version. Use CTRL+F to find it)
And replace it with this:
And that's it. You are all set. From now on, all the additional product pictures will be visible in the category browse page.
You might also consider to change that number "1" to "3" or "5" instead of completely eliminating, so that many product pictures will be visible only in the category browse page. For instance, if some of your product has 10 additional pictures, it would make sense to make that number 4 or 5, so there won't be any layout corruption in the browse page.