Any team who breaks any rule should be reprimanded. As tough as it is, it's necessary to preserve the integrity of the program as a whole, from team to team, competition to competition, season to season. Now, before I get jumped on for that, I'll say there shouldn't be any "one size fits all" punishment to be handed out whenever anyone cries foul. I'm of the firm belief the punishment should befit the crime.
There are already well documented
rules and policies in place regarding on-field competition, and the referee crew does a great job of enforcing and distributing punishments for infractions. For those who don't know, most penalties during a match incur flags to be thrown. The number of flags depends on the offense, and by the 2004 rules, each flag is a 10 point penalty. More severe penalties will merit disqualification and/or disabling of the offending team's robot. Rule G32 in particular showcases perhaps the most severe documented FIRST penalty- disqualification from the remainder of the regional competition and/or championship event.
Realistically, it's only on-field where any potentially cheating team has the highest chance of getting caught. Not only are there well qualified volunteers on the field, but various FIRST officials, Innovation First staff, and any number of eyes which could spy some mechanism or part which is obviously illegal, should a team try to pull a fast one after successfully competing inspection.
Outside of that, the only proof of any other types of cheating would be here-say or testimony of other teams/individuals, which unless accompanied by a significant multi-team backing or documented/photo proof, isn't necessarily viable evidence.
Now, for the real meat. I'd brand any (off field/not otherwise documented) offense as one of three possible categories- minor, major, severe. Examples of minor offenses would be smuggling small/non critical post-ship fabricated parts into competition, working on parts in a hotel room, essentially things generally seen as wrong, but not large enough scale to modify the outcome of the competition. Minor infractions should incur a minor penalty, say 5 or 10% off ranking points, or score, or whatever method of determining rank is.
Major offenses would modify the outcome of a match, but in a rectifiable manor. This would include using known illegal parts post-inspection. If incurred during the qualification rounds, the team would automatically be disqualified from it's next 2 matches, or if in eliminations, automatically dropped from it's 3 team alliance (where the other 2 members can pick another 3rd partner).
Severe infractions I'd rather not think about. They would undeniably affect the outcome of a match, and/or the competition, and would be so devoid of gracious professionalism and of such conduct I personally wouldn't care to see these teams in any future competition for the remainder of the season. Examples would be sabotage of an opposing alliance's robots, stealing parts/tools from other teams, and violence (fighting, excessive verbal abuse).
I know in each scenario there's the chance it may only be a few individuals, and may not necessarily reflect on the team as a whole, but I'll apply the general concept from these forums. People who post here (whether they disclaim it or not) do reflect where they're coming from, and do to an extent, represent their team. If 2 or 3 people smuggle some parts into competition, they're smuggling them on behalf of their team (if they didn't have a team, what would they be doing with parts in a hotel room?). Similarly, if a team member intentionally damages another team's robot, he/she does so as a member of his/her team, and it does reflect on the team as a whole, and as such, the punishment is reflected back.
I know people will say disqualification is not the answer, because it deprives teams of the chance to compete and be inspired and such, but there's no inspiration to be found in cheating. There may be a slight feeling of triumph for a while, taking the ski lift to the top of the mountain while others climb with ice-piks and rope. But there's no better feeling in the world than knowing you did your best, produced an amazing piece of technology, and learned more than you thought possible. All the while watching your growing potential take the field and pick up balls, cap goals, and hang from a bar taller than anyone out there. Shortcuts are just that- short, and I'd feel cheated if my robot won, but I knew it didn't deserve to.