IMO they’re just frauds. It takes zero experience or qualifications to call yourself a sleep consultant, anybody could set up an Instagram and advertise themselves as one.
I would very much steer clear of any ‘consultant’ that claims they can help ‘fix’ your child’s sleep. It isn’t one size fits all OP, no two babies are the same.
may I ask how old your child is? The bit about bath and milk tells me they are still a baby? Honestly I get how hard it is, it’s exhausting but there are a million reasons as to why your baby isn’t sleeping, and there is not one single “sleep consultant” on this planet that can give you answers
it could be teething, brain development, too hot, too cold, wake windows, over stimulated, under stimulated, hungry, not feeling right, 100 other million things
babies are biologically meant to wake up overnight. Nobody wants to hear this and sleep consultants certainly won’t tell you this because what would they then be able to sell?