Once you are ‘in’ you must not be surprised if occasionally the tables turned; people are as likely to ask you questions as you are to ask them, so be prepared to answer them as you can. Being evasive and mysterious can seriously damage any rapport you establish. There is nothing wrong with admitting you are there as a researcher, in fact I take the stance that it is essential to admit your motivation. There is a long running debate on the rights and wrongs of covert or overt research. When it comes to recommending an approach I always recommend overt research (when it comes to my students I insist on it). You are who you are and you have a purpose in this place; honesty will get you further than deception every time.