You might find it hard to believe, but that does not happen to me, like that. Now, that there is a chance that they may "adjust" the price to get me in or out before it happens is, I suppose, possible, but I do not think so and I have not had to phone mine up over that sort of complaint in the 20 odd years I have used them.
I cannot say that about IG, who I have rung on more than one occasion., in the days of telephone trading and minimum of 10 GBP/point. Overnight trading was, particularly, dangerous and I gave that up immediately.
I do believe that competition has improved matters a lot over the years since then but it is best to be watchful and realise that these people are not angels. Neither are we, all, angels, either and they would br out of business very quickly if they took us to be.