Since you're dealing with a hoarder, the chances of success are minimal to begin with. Even if it is a family member, friend, church member, or whoever, consider if getting involved is the best thing to do. Nothing stings more than doing a favor for someone only to find out later that they have been complaining to others about the incomplete job you’ve done. Since you aren’t there to defend yourself it is impossible to set the record straight that it wasn’t you, rather it was their actions (or lack of them) that caused the problem to continue.
If you do decide to help, here are some basics to keep in mind:
The first step in any commensal rodent job is to remove the food and harborage as much as possible. The key to success is for the client to keep the area clean of these items (i.e., perform basic sanitation actions).
The second step would be to use a combination trap/rodenticide treatment to knockdown the population level. For traps, you can use multi-catch mouse traps, glue traps or snap traps. As with all types of trapping, everyone will have their favorite types of traps to use. Push button or T-Rex style traps (these are generally plastic style traps) are very easy to set and remove caught mice from while strike bar style traps may be more difficult. Based on who is tending the traps and how they are baited, may determine the type of traps used. For plastic style traps, consider using commercial bait such as Provoke (which is what the traps are manufactured for anyway). When working with thin pans, use cotton balls firmly attached to the pan. For wide pans, use a food bait/lure. Regardless of the trap, location and proper trap placement will have more to do with success than the type of trap used. Despite public opinion, there is a correct way and an incorrect way to place a mouse trap.
The third step is to perform exclusion / repair services to keep the rodents out. Check for openings not just at ground level but also up to and on the roof and remove/repair what you can. Rodents will easily chew through silicon, so use a commercial grade sealant instead on cracks.
We recommend installing/maintaining rodenticide feeding stations outside of the structure for our fourth step. This allows treatment of potential animals before they can become established inside the structure and acts as a monitoring system which is the fifth step of a successful program.