Participants in a user trial need to represent the target audience. Participants for an expert test need to have an appropriate type and level of experience and skill.
It is preferable they have no prior knowledge of the product that is under review.
Some participants will expect a fee. This needs to be negotiated with the client or production team, as this cost needs to be factored into the budget.
It is important to match the participants carefully with the product purpose and ensure there is a range of people. Sex (male and female), computer and internet literacy (poor and good) and language literacy (low and high) will generally be a range consideration within the sample group. Other ranges may include education (secondary or tertiary), residential address (rural or metropolitan, local or overseas), employment (full-time or unemployed), income (low or high) and job position (blue collar or white collar).
It is sufficient to invite between five to ten participants to a trial. It is not the number of participants that is important, it's the quality of their comments.
You need to remember that not all the comments made will be valid. The comments need to be assessed against who the person is. For example, someone may say that the product is extremely difficult to navigate, whereas other participants do not find it so. It is only when the person's low literacy skills are identified that the poor navigation is meaningful.
For an expert test the participants need to be from a specialist expert area: graphic designer, content specialist, instructional designer, programmer, navigation designer, animator, 3D graphics or musician. They will be inevitably looking at the product from their particular viewpoint.
Your choice of expert team members will reflect the nature and purpose of the product, and you will need to ensure that the test team represents a broad approach. It is recommended that a minimum of three people be on an expert test team.
Work with your buddy to select the participants for your user trial. You need to have at least five. The participants will be used for both your and your buddy's sites. Make sure they represent the target audience of your project sites.