The most important thing is to keep a proper form, even if it has to be done with lower weight. Personally, I think that doing excessive weight just for the sake of the weight and not proper form is completely unprofessional, especially on behalf of a trainer. First of all, there is a higher chance of getting an injury by taking more weight than you can handle with proper form. Secondly, it is pointless, since you are not stretching your muscles, and there is no real breakdown leading to hypertrophy.