I know that may sound strange coming from a person who has been an online Keyholder before (and will be again) but I have recently become aware of some rather unscrupulous women (or possibly men) who would take you for all you are worth and leave you... Frustrated!
If a Keyholder demands that you purchase toys for her use (on you) from her (or from a specific website) you might want to watch your step. Asking you pay up to $900us or MORE for toys doesn't sound quite right to me. That's a great deal of YOUR money out of your pocket for who knows what!? It is not unreasonable for a Keyholder to want you to have certain toys at her disposal. However, there are always substitutes you can use or purchase.
If your prospective Mistress demands that you close all your “other” website accounts in favor of her own, or any specific website, she may be asking too much. After all, were you wanting this to be a permanent thing? Or were you just wanting to test the waters to see if she is the right Mistress for you? It's okay if she wants you to open a special website account on her (or any other website, but unless you are sure that she is “the one” for you, you may want to look elsewhere for a Keyholder.
If she immediately wants to take command of you and all you do, be careful. She make make other demands that are outside your limits later on. If she wants you to give her information about yourself that you would rather she (anyone else) not know, again, be careful. Personal, private information can turn out to be used for blackmail purposes. You don't want to get caught up in something like that.
Don't give out information about your personal finances, people you know (such as family or friends), and never give out your real address. If she wants you to give her your phone number, buy a cheap phone and use a service such as Net-10 or Straight-Talk, something you can walk into a gas station and purchase a time card for.
If she wants you to use something such as Skype, Yahoo messenger, or other video chat program, be extremely careful about what can be seen (or heard) in the background. Even letting her see your face (especially if she records your sessions) or required you send photos, can be devastating once she publishes them online. Once she has such photos, she can do anything she likes with them! Be aware of that!
You should be allowed to interview her for the job as much as she can you. Don't sign up with anyone who won't answer questions or allow you to have personal limits.