I didn't even have to read all the comments on this and can see how uneducated some people are about this specific issue. It is a CIVIL RIGHTS VIOLATION to even ATTEMPT to ask for paperwork, attempt to get any deposit or require ANY documentation to confirm the validity of any training or medical condition of the possible tenant. How do I know? I have a service dog (disabled veteran here). As was suggested by a couple other people on here, the ONLY alternative is to find a more qualified tenant and rent to them instead. There is absolutely NO paperwork required under federal law to even certify any training was successfully completed. Many people believe otherwise, but that is not the case (meaning it's not the case that paperwork is required). Why? Because there are MANY disabled Americans (obviously not just veterans) who have owner-trained service dogs and these "teams" are accepted under the ADA as legitimate service dog teams. Why? Because not every 'team" has the option to enter into a formal program for training. As a matter of fact, there is a rather lengthy waiting list for the few programs to actually do exist and that waiting list can be as long as 24 months. The closest training program that I found for me (at the time I was searching a few years back) was HOURS away and out-of-state at that.
As mentioned on here, federal law trumps local law. That last thing you want is a lawsuit for a violation of the FHA (Fair Housing Act) and ADA. Many legitimate service dog "teams" get a bad wrap because of the fake teams that are out there. Under federal law there are only 2 questions any one can legally ask to any service dog handler. 1. Is the dog a service dog required because of a disability? 2. What task is the service dog trained to perform? The response to this question can literally and LEGALLY be as vague as "My dog provides a medical alert for a medical condition that is private in nature". Anything above and beyond this (unless volunteered by the disabled person) is a civil rights violation. One of the key reasons that breed is so passionately contested is because federal law does not exclude any breed from being a service dog. As a matter of fact, countless veterans with PTSD have successfully trained (yes, even owner trained) pit bulls and other less "desirable" breeds to be their service dogs and even gone to the point of rescuing them from shelters.
If a lawsuit were pushed all the way, an insurance company can be found in violation of the ADA for dropping insurance because of a pit bull or G shepherds since they're NOT legally pets. I don't know how many disabled "teams" have taken it that far, but I've sat in more than my fair share of classes to know this by heart. Part of the problem is that there is no blanket standard across the board and the only one (blanket standard) that DOES exist across the board is so vague that it typically prompts emotionally discussion across the board because of those who are inexperienced in this aspect of the quality of life for the disabled typically stereotype the legitimate disabled community with the fakers that are out there. Then the disabled community that's legitimate responds back in anger because we're convinced that the rest of community that is not disabled isn't understanding of the disability and/or is lumping us in the fake service dogs. BOTH sides need to come together. One of the things that the disabled veteran community is STRONGLY encouraged to do is to take the time to help encourage and expose those that ask legitimate and sincere questions and educate them. Many times, it's just a matter of a sincere misunderstanding and the person who's asking the questions genuinely hasn't be familiarized with federal law. HOWEVER, since anxiety is a legitimate medical condition with which a service dog can be required, many times, just the approach of the discussion prompts a panic attack since the questioner (in some cases) is less than cordial in their asking OR the service dog handler anticipates a confrontation that may never take place in the first place.
For the person (@ Scott Schultz) you can NOT ask for documentation because there is NONE required under federal law. Federal law trumps state law. @ Alvin Sylvain, the former (service animal) is NOT always fully trained because they have to be in the public in order to be trained in the first place. How do you think the puppy gets trained? In a private setting to get ready to go into the public? This is one of the very reasons why this is such a contested topic in so many arenas and ways because so FEW people actually understand this. The BEST way to assess if a dog is a service dog is to see how it responds to other dogs. Many dogs are territorial, HOWEVER, the method I'm describing here is nowhere NEAR full proof because if there is a service dog in training, that dog could literally be adjusting to the public that it's being trained to take care of it's handler in. You can NOT just "know" which one you're dealing with. Since the federal law does NOT provide specific guidelines for service dogs and "teams", there's no way that local communities can try to implement any rules that federal law doesn't recognize at all.
@ Calvin Ozanick, you can NOT request documentation "for the animal in question" because under federal law, there IS NO documentation required.
Since owner trained service dog "teams" cannot make it to training facilities, the federal law recognizes this AS WELL AS the fact that there is such a long waiting list and countless disabled Americans do not have the time to wait as long as 2 years to get a service dog. THAT is one of the reasons why the federal law is written the way it is.
IF you do try to charge a security deposit for a service dog "team", I wouldn't even want to be standing beside you in court when the judge hands your head to you on a platter. In the highly unlikely event that the local jurisdiction isn't familiar with the law (some law police are not familiar with the law), than any higher court that sees this case on appeal will GLADLY make sure you never make this same mistake again. For those naïve enough to attempt to quote Wisconsin or any other state law, they have NO experience with the federal law, which I notice NO ONE is quoting here. The fact that there are even posts on here alleging "BS" shows the stereotypical response from countless people who draw conclusions before getting all the facts. Absolutely disappointing coming from investors.
In the end, I hope this answers the OPs question. I know some of my post is redundant, but so are some of the responses that I'm seeing to the OP. I'm passionate about this topic for pretty obvious reasons. Medically retired Marine Corps veteran here.