Core Boarding Vaccines
There are 3 must have vaccines when boarding dogs:
Being vaccinated helps prevent spread of disease, it would be awful for one animal to infect the rest of the pack. These viruses can be fatal (though unlikely with kennel cough) and spread like wildfire.
Note: the vaccine protocol can change depending on your location globally, this is specific to Canada
Can I ask for the phone number of their vet, and expect the vet to tell me?
Yes and no, depending on where you live there can be privacy laws where the owner of the pet needs to give permission to the hospital to release records on their behalf. This can make things complicated as not everyone is compliant with calling the hospital.
Do I have to ask for documentation and check it myself?
This is the best way to do it, hospitals generally give out vaccination certificates (example) which are also signed by the veterinarian who has done said vaccines. Ask for a signed certificate and make a copy for personal records (liability).
If you plan on making this a full time gig I highly recommend getting insurance to cover for any potential lawsuits, damage to your property, injury to the animal etc. Having insurance gives a peace of mind to the client.
I would also have a lawyer create a document for your for the client to sign (i.e Client states that all the information provided was correct etc..) this is to cover your butt in case of forgery of certificates causing illness in other pets etc.