In that case, you simply need to email back before signing with the changes you need made. The company will do that to you if they get something wrong (wrong start date, incorrect pay or bonus percentage), so it is completely reasonable to have a conversation about what adjustments you need made to your contract. The worst they can say is no. And if they say no, that's a sign that you should really think about what you are signing.

A fundamental of negotiations (and human relationships) is not wanting to create problems or appear to be a 'trouble-maker'.

In a recent personal situation, it was obvious serious mistakes were being made and it was obvious what the solution was - painful, but certainly better than the alternative. However, we hadn't yet experienced the consequences, and predictably another other party railed at me for making things unnecessarily complicated.

Employees at businesses don't want to be seen as trouble-makers and have their offers rescinded.

A (manipulative) trick to negotiations is to put the other person in the position of being the trouble-maker.