Beggars can't be choosers
People who depend on the generosity of others are in no position to dictate what others give them.
Idioms and Phrases with beggars can't be choosers
Those in dire need must be content with what they get. For example, The cheapest model will have to do—beggars can't be choosers. This expression was familiar enough to be included in John Heywood's 1546 collection of proverbs.