If you spend much time in the Drupal community you'll hear the refrain don't hack core. But no matter how many times it might be said the temptation to hack core seems great. We've recently helped with several sites and there seems to be a common thread of problems caused by hacking core. These hacks are then costly to the client in the long run, often resulting in several hours (at best) of additional work to sort out what has been done and set things right.

My contractor says they need to hack core

So you've heard you shouldn't hack core and now you have a developer that is telling you they must do it to accomplish your goals. Please, Please, Please when you hear this do yourself a big favor and say no. If the contractor you're working with still says it's necessary then by all means get a second opinion. There are many, many, many, manyThis is the firm I started and own., reputable Drupal consulting firms who will help you figure out whether the hacks to core are really necessary.In addition to consulting firms there are a number of outlets like forums and local Drupal groups who would also likely have people willing to give you some suggestions The money you spend hiring one of these groups for a couple of hours will be well worth it in the long run. Read more about Don't hack core and don't hack contrib (unless you have to)