That would be unlikely. I would be concerned if they did do that because of ethical concerns.
Just so everyone is clear on this, I have a financial interest in this answer, as I practice in this area of the law.
Let's take a look at each issue separately.
when finding a lawyer to help with my PEB what are the odds of finding one that will somehow guarantee an outcome
If an attorney does this, it is pretty clearly unethical and prohibited by Rules of Professional Conduct. This is because it is misleading (you can't know how the PEB will rule and thus cannot make guarantees) and it violates ABA Rules for Professional Conduct "Rule 7.1 Communications Concerning A Lawyer's Services-A lawyer shall not make a false or misleading communication about the lawyer or the lawyer's services. A communication is false or misleading if it contains a material misrepresentation of fact or law, or omits a fact necessary to make the statement considered as a whole not materially misleading."
or discounted fees for not meeting that guarantee?
For the reasons mentioned above, the guarantee part is out. But you could find a lawyer who may take a contingency fee. Something like, "I will charge you $5000 if you get 30% or more, but only $2000 if you don't."
While technically permitted, it is still problematic, in my opinion. Here is why. When setting a fee, a lawyer takes into account the value of his work and the overhead of running the business. He then comes to what he thinks is a reasonable figure for his services, also taking into account the work involved, his expertise, and what his competitors charge. That figure is
x. Now, if he takes a contingency fee, he must be either optimistic about the outcome and is willing to price in the risk as
y (the amount he is willing to discount if you don't get the result you contracted for), or he is pricing in an increase in his fee,
z (the amount above x he is going to charge in order to make sure he gets to x, no matter what happens). So, if he loses and only gets
x-y, he is getting less than he needs to stay in business. Not a good deal for him and unless he is very confident, not a deal he will likely make. If he charges
x+
z, but loses, and only gets
x, (what he would have charged in the first place) he has gotten more business than he would have otherwise, made his standard fee and has no incentive to work any harder than under the normal agreement (which I believe is what you would be hoping to get by having the contingency arrangement). But if he wins and gets
x +
z, now he is doing great, and he probably did the same work he would have done anyway. But you just got charged a premium for the willingness to take the contingency fee and probably just paid an unreasonable fee. Two of the outcomes in this arrangement are good for the lawyer while only one is good for you (and the attorney won't take it unless he is sure in the first place).
What I always suggest is that you speak with several attorneys and choose who you feel most comfortable with based on their experience in this area of the law, services offered, and fee. However, I would have serious concerns about anyone who offered a guarantee or took a contingency fee in these matters. Contingency fees tend to lend themselves more to getting a percentage of a recovery, and are probably most appropriate where the hourly attorneys fees would otherwise be very large, and the potential recovery is substantial.