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Choose outsourced help that has a process which matches your own. This results in less pain. To ensure you don't get ripped off, try to negotiate as fixed price contract for the outsourcing. Then the risk is put in the hands of the outsourcing company.
Exercise caution when you grow the outsourcing effort. Also watch out for expensive tool choices by the outsourcing company. They may not have your best interests at heart. More importantly, the costs of the tool might be prohibitive. Luckily our own project has a good sized test team. They also have some really good talent. So far they have only outsourced a little work to other employees in our own company. They have been short term engagements. But you never know. We might look outside for some help to test.