The law is different all over the world. (Here in the UK, there are even substantial differences between the laws of England and those of Scotland). So you need to ensure that your research takes you to answers that apply in your own country.
Your use of dollars in your question suggests that you might be in the USA. If so, this is the leading Q&A sites for your own country:
https://answers.yahoo.com/
(Up until recently I would have also included Answerbag.com but it seems that it has now closed down).
For what it's worth though, here are the key points under English law:
http://www.seqlegal.com/blog/10-key-facts-about-english-contract-law