It’s not a secret that developers can earn money by chrome extension selling, but not a lot of us knows how to make the deal safety with a guaranty of successful completion. Good news for us that Chrome store has its own form for transferring extension. It means in case of any question you can contact support or open dispute and receive needed answers. I would like to point out that having some documents to help tech support with clarifying this case will work to your benefit.
First of all I recommend to sign up a legal agreement for chrome extension selling between buyer and seller to protect rights of both sides. It will free you from unnecessary worries and ensure your rights.
What will be better to think about if chrome extension selling means giving an access to developer account without filling a Chrome transferring form? World wide practice to use certified online services for money transfer is a good option to prevent a fraud during chrome extension selling process. Usually such services hold on the payment until all conditions will be met. It minimize risks to have difficulties with transferring money and extension. 
As Chrome extension selling can be done using online services, as well can be sold add-ons, toolbars and plugins.
In conclusion, allow me to recall that chrome extension selling process will be finished successfully if you stick to two simple rule: sign up a legal agreement and use online services for money transfer that are guaranty of safeness and legality.