So what prevents them from colluding?

那他们为什么不能串通
One thing they could do, presumably,

他们或许可以
is they could write a contract, these firms.

签订一个合同
They could say I won't lower my prices if you don't lower your prices,

可以协定好你不降价我就不降
and they could put this contract in with the pricy lawyer,

然后可以找个刚处理完离婚纠纷的
who's taking a day off from the divorce court,

著名律师来作见证人
and that would secure that they wouldn't lower prices on each other.

那样他们就放心对方不会打价格战了
Is that right? So why wouldn't that work?

是这样吗为什么这么做不行
Why wouldn't writing a contract here work?

为什么他们不能签这样的合同
It's against the law. It's an illegal contract.

因为那是违法的这是个无效合同
What about you with your roommates?

那你和你室友是不是可以签协议
How many of you have a written contract,

有人写过协议吗