Can you provide a link to the page where you're seeing it?

(It's much easier to troubleshoot and help.)

What version of Market Theme are you using?

Is it Market version 3.61, or is it later than that?

If it's version 3.61, then in your Market Theme settings area — there is a setting for the number of products per row for the grid-view template that should be changed from 6 to 4.

Then, in your grid-view template (frontdoor.php if you're using version 3.61) you'll need to add a "height" setting.

Line #68 should say something like:

<div class="post" id="post-<?php the_ID(); ?>" style="width: <?php echo $mkt_options['mkt_thumbnail_width']+10; ?>px;">

If you change that to something like this:

<div class="post" id="post-<?php the_ID(); ?>" style="width: <?php echo $mkt_options['mkt_thumbnail_width']+10; ?>px;height:245px">

and save the file, and I think that should do it.  This will force the heights of all the boxes to be equal.

Also…  If you have multiple copies of the grid-view page template for each of your product categories, then you'll need to do this last change for each of them.

Let me know how it goes.

Very good.