Can one buy after Pesach flour from a Jewish store that may not have sold the Chametz properly?

See Shulchan Aruch (O.H. 453: 4) and Mishna Berura (ibid 24). Horav Shlomo Miller’s Shlit’a opinion is that one should not use that flour, since it is very likely that the flour was made from washed and thus fermented wheat grains. However, in need the Rov permits if additional doubts could be added to the prohibition. Nevertheless, Orchos Rabbenu (2: 24:25) permits in our days its use.