Some countries, such as the UK and Australia require service dogs to come from programs recognized by ADI.
In the U.S., there is no national mechanism in place for certifying or licensing service dogs. Some programs certify the dogs they train, but very few will certify dogs trained by others for liability reasons. Certification is not necessary so long as the handler is legally disabled and the dog is legally trained as a service dog (which includes task training).
While a business cannot require certification as a condition of allowing a team to enter their facilities, they may ask what the dog has been trained to do and whether it is required because of a disability. Refusal to answer can result in access denial. If the owner does not answer "the task question" or the dog does not behave appropriately, regardless of whether it has a certificate, the business may have the dog removed.
There are some fly-by-night agencies that will sell "certification" to anyone for a fee: they are a waste of money. Unless the team are examined in person by a qualified evaluator the certificate might just as well be printed on a home computer and laminated, which is exactly what is done by the agencies that sell certification for $40-$250. If you've got to have such a certificate, make your own and save $39 or more.
Remember: certification doesn't make a dog a real service dog any more than a fake ID makes a minor over 21. What makes a dog a real service dog is being trained to perform tasks that mitigate his disabled handler's disability.