Ref: http://fallout.wikia.com/wiki/Fallout_4_merchants
Anne Hargraves was hired without any problem.
But after that Trader Rylee and Doc Anderson never showed up. The suggested console commands in wiki referred to, made them show up though and when assigned to shops they have stayed until now. So console commands are necessary? Or is it just that they don't really mean what they say about working in settlement?