There are some stain types that you will find mentioned in many articles about carpet cleaning, and some that are less common.
If you ask professional carpet cleaners what stains they get asked to advise on and to remove, they will certainly have stains that they are more frequently contacted about than others. We are sure that one such stain which is far more common than others is red wine.
Whilst tea, coffee, paint, and nail varnish will frequently be the cause of the problem, it is red wine that seems to cause the most consternation amongst homeowners when it gets spilled on their carpet, and worse, it dries and stains the carpet.