1. Many companies that charge by the square foot will charge you for the space under the furniture, even if they don't move any. In other words, if your room is 12' x 12', they will charge you for 144 sq. ft. If there happens to be furniture in the room, you could be paying 10% to 30% more than you should be!
2. Chances of getting a novice carpet cleaning technician are pretty good, especially if you are dealing with a larger company. Novice technicians have an improper wand stroke, meaning they leave areas of the carpet that have either not been cleaned or that are too wet.
3. Improper knowledge of chemicals is very common, even with experienced carpet cleaners. Many technicians will just try one chemical after another, until they find something that works! This is very bad because the wrong chemical will set the stain instead of removing it, resulting in permanent damage of your carpet, in which you will foot the bill for when you have to replace it!
4. One thing you should never do is leave a carpet cleaning technician in your home by his/herself. This gives them every opportunity to take short cuts and save time, so they can fit more jobs in per day, to get paid more money. This will also be at your expense! Unless you have had a long personal relationship with one particular cleaner, I wouldn't do it!
5. Never agree to get scotchguard or teflon protector applied to your carpets, unless you see the original container with the seal still intact. Many times this will merely be tap water mixed with very little protector. Also, a pump up sprayer is not sufficient to apply the chemical. The water pressure needs to be at least 45psi, which can only be achieved if they have a spray attachment hooked to the same machine they are cleaning your carpets with. The most common is a "hydroforce sprayer."
6. Many times you will get a quoted price for carpet cleaning, but when the cleaners arrive, you will find that the price has suddenly changed due to conditions that weren't expected. This is an attempt for them to take more of your hard earned money than they should. Make sure you find out what the service includes before you agree to the cleaning.
7. warranty. Most will tell you that the chemicals they use are safe, but really are not. They use what cleans the carpet faster and saves them time. Of course, if they void the warranty using chemicals that have ph levels that are too high, you will not be able to replace the carpet, unless you pay out of pocket. This applies to nylon or polyester carpet, not olefin. (berber)
8. Dry cleaning companies that vacuum, then pre-spray, and then use a bonnet with a buffer (floor machine) to clean the carpet, only cleans the surface. So how do they get the rest of the chemicals out of the carpet after they are done? They don't! It stays in the carpet and sometimes yellows or browns the carpet because of the high ph level in the pre-spray. It will also dirty the carpet faster. Steam cleaning is the most recommended form of carpet cleaning and is also the most effective.