Whats the meaning to sell a bitcoin address when you are not safe to use a bought address because someone else can spend your money. The best way is to generate yourself the address and use only you.
No, someone cannot spend your money.
For instance, let's take an example of bitaddress.org, You can't actually generate the desired vanity address until you have both the partial-private keys. You merge them and then you get a new private key which carries the address of your choice. The third party never has access to your partial-private key, so he never has access to your vanity address private key.
This is before you own that address because until then nobody is using that address, but vanity address are only used to have a custom prefix <10 characters which is not hard for someone else to generate. I think that OP is talking about sharing the private key with someone else which is a worse idea.