Although a business card can be an acceptable trademark specimen for services (classes 35-45), we usually don't recommend this option to clients.
Business cards usually don't include all the information to fulfil all the requirements for an acceptable specimen. Many times, they miss a clear description of the services offered.
One of the requirements for trademark specimens for services states that the specimen must include a clear reference to the applied-for services and show the mark associated with these services.
For services, we usually recommend clients submit a website screenshot or advertising material since these will naturally include a proper service description.
Please note that a business card is never an acceptable specimen for goods (classes 1-34).
You can find examples of acceptable and unacceptable specimens for your niche in our Specimen guide.