what are those tools that dealerships have available? how can a customer be 100% certain that rear passenger seats are now completely dry inside out? what recourse does customer have to refuse to take the vehicle back if he/she is not 100% certain the car that leaked rainwater into interior is up to standards?
The weather shouldn't matter, they work on the vehicle inside where it's warm. Basically parts are removed and industrial or heavy duty driers and dehumidifiers are used, inside and outside respectively. When the dealer tells you the car has been repaired and is "ready" go check it out. (before accepting it) See what parts are listed as being replaced. Since you know what areas were wet check them out to make sure they are dry, ask what exactly was done to dry it and mitigate any potential mold. They may have used a disinfectant spray too. If the advisor is vague, ask to speak to the tech who worked on it. If you find something is still damp then point it out and ask them to please keep the car until it is repaired properly.
When you take the car back into your possession keep and eye on it and make sure its still not leaking (sometimes leaks come from more than one place and they may have found only the first one as happened to me.) If you smell a mildew or damp smell, then take it right back and put it back into the service department.
What I did is get the service manager and then the general manager involved and stated my case, the trunk padding was slightly damp and wasn't replaced. I stood my ground, pointed the area out to them and made a fuss that I didn't want to take a car back that had the potential to become a mold problem. They kept it longer and replaced some of the padding. By this time (along with a host of other problems the car had) it had already been in shop long enough to meet the qualifications of a lemon.
Your circumstances maybe different but the main thing is to advocate for yourself and sometimes that means getting insistent, going to the dealer principles, and not taking no for an answer. Personally, I could care less if they think I'm a nut, just so long as things are done properly.
I understand the frustration with this kind of repair and my advice and statements aren't meant to be condescending or anything. Dealing with a dealership is hard for many people, so I'm just trying to help. A good dealership will not only try to get the repair done right the first time (they are judged by surveys etc.) but they will want to keep their customer happy so they purchase again. I've worked for many good dealers and dealt with many who weren't so good, who unfortunately can give the whole industry a bad reputation. Hopefully some others on here (this place is a wealth of information) will have some more advice and information to help you. Good luck and keep us informed.