If their interests are things that they choose to type into the fields, then it's going to be extremely hard to match anything up, as computers look for patterns that match and "going on vacation" and "taking trips" are interest matches, but a computer will see them as two unrelated items. Hopefully you've taken that into consideration.
To make the match not come out the same each time means you will need to add fields in your database to keep track of the last matches so you can check them against the new match and see if it was used before.