If you are selling on eBay and receiving large amounts at once than.. (Limited.) If you are sending and receiving money a lot of the time... (Limited.) Pretty much just keep providing documents when they limit your account, and eventually they will run out of things to ask you for. Of course this could also be due to you logging in from different computers (Ip's) or using a proxy. This can be interpreted as someone breaking into your account, and sending money without authorization.