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It's not clear what kind of relationship you're referring to here. A shelter vet who works for a shelter wouldn't be charging money, they'd just be another employee. If this is a vet with their own practice who is providing discounted services for you, they can provide anything they want, or not. It's a donation of time and/or services. What a vet provides a rescue or shelter is up to you and them to work out amongst yourselves. There's no standard package or recommendations.
It's a constant struggle now for nonprofits to find and retain vets who are willing to provide discounted or any services at all because there a huge nationwide vet shortage, and they simply don't have the bandwidth to provide free or low cost services. Or they don't want to because they can't even keep up with all the paying customers.