We've found a couple who want to let my old flat (this is the first time we've let anything, so total beginners). They've spent the weekend haggling over price, furnishings and number of weeks deposit required. Now they say only one of them wants to be on the tenancy and be reference checked by the agency as the other has no credit history (not a negative history, just no history). This makes us nervous. Should we insist both get checked or is this normal practice?