curious about floor vents

Has anyone here had problems w/floor vents -- for example, getting water and/or sand in them? We had trouble years ago w/drainage in our yard, so we put in French and surface drains, and then had our floor vents cleaned and repaired. We also got a whole house air cleaner, so we have no more problems (allergies/health). Well....We are looking at another house in the neighborhood (for sale), and it has about four inches of sand in one of the floor vents! The house is in poor shape, in general. It's 30 years old, and needs some major cosmetic help. However, we're hoping it's okay structurally. The current owner is out of state, and will probably let it go fairly cheaply. But if this sandy vent is a real problem, then we're NOT interested. I have heard we can get someone to check the vents w/some kind of video? Anyone familiar w/this? And is this a reliable way to check? I just don't want the house if it's really going to be a huge (expensive!) problem. But it's a really nice, big house w/a pool, w/great views. We could use a bigger house (we have five kids!). My husband isn't thrilled w/the amount of work, though.... JoAnn