You would think so, but if Dortmund try sticking to their guns with their new valuation and would-be suitors spend their money elsewhere as a result, Dortmund could be left with a resentful Bellingham on their books in September. If United or PSG were the only clubs willing to spend the asking price, they can't force him to go to a club he doesn't want to go to, he could run his contract out.
If Dortmund declare no less than £150mill and Real Madrid, Liverpool, or anywhere else he might like to go refuse to pay that much, and spend their transfer money elsewhere, Dortmund can't say on August 29th "OK, you can have him for £100mill" because then the money will already have been spent.
I think a game of transfer chicken might work out bad in Dortmund's case.