We have done the after builders cleaning both ways. It is all about your preference and time restrict for the job. Here are the things that you should consider before you make your final decision. 1. Before the carpets are fitted: This way all the dust and dirt underneath will be cleaned and will not go into the carpets after that. However, please note that some amount of dust will accumulate on the surfaces after the fitting of the carpets. 2. After the carpets are fitted: There will be dust under the carpets (unless you do not clean it first) which over time will get into the carpets. Once you clean the carpets professionally it is possible the dirt to get into the fabric and dark marks to appear. But it all depends on the carpet fabric and how much dust or dirt will be underneath. Frequently asked questions about After Builders Cleaning