While there is a mitzvah to give tzedakah -- as per the Rambam's list
Not to refrain from maintaining a poor man and giving him what he needs (Deut. 15:7)
To give charity according to one's means (Deut. 15:11)
is there a mitzvah to accept it once it is offered to you? If I don't think I need it (or that others need it more), or if I object to the source (money donated by someone whose practices I find incorrect), do I have any obligation to accept it? [and would my refusal take away a giver's fulfilling a mitzvah?]
Certainly if I need the money to survive, a refusal to accept it, putting my health/life in danger, would be a problem and if I reject it publicly, there might be a problem embarrassing a donor but in cases that aren't that extreme is there an obligation, a mitzvah or some other level of expectation?