Expand the Current Process
Legal labyrinths are fun, but the more realism involved, the more games get bogged down.
Perhaps, rather than representing the process with a single roll, a series of rolls would suffice. These checks would be built in such a way as to reveal progressively more about the risks involved with the contract.
Some skills, such as Sense Motive, may be useful throughout, but try to vary the required skills for each section so that different characters and attributes are useful in different phases.
For greater results, have the players declare which skill they are using and use different charts for each skill, allowing differing levels of disclosure. You could even make the individual snippets of the contract (gathered through successful checks) on little slips of paper, thus letting the players "read between the lines" after the necessary skill checks are made.
(We, the adventurers, heretofore known as THE PARTY, agree to...)
Skills: Knowledge: Religion, Knowledge: Nobility, Bluff, Sense Motive
10+: This section is setting out who is involved in the deal and what the penalties are for breach of contract. You don't see anything too shady here.
15+: Some of the wording here is a little suspect. You see that the contract devil has set up a situation where he will not need to fulfill the contract if the party actively opposes the chain devil's other interests.
20+: [Appropriate party member] is actually entitled to 20% less recompense due to certain clauses in the contract. This portion goes to the contract devil, for 'services rendered in or around a twenty year period preceding or following the signing of this contract.'
(Mr. Mephistopholes, hereafter THE CONTRACTOR, does hereby agree save in the events outlined in SECTION I, to provide the following services....)
Skills: Sense Motive, Knowledge: Local, Knowledge: Nature
10+: The devil is offering to provide you information pertinent to your quest along with the opportunity for future business deals at preferred rates.
15+: There are some problems with this. There is no guarantee that the provided information is unknown to you, for instance.
20+: The devil is offering some services that are couched as beneficial but may not be. 'THE PARTY shall be protected from transgressions or contact with nonsentient natural flora to a radius of 1000 feet at all times for a period of six years.'
(THE PARTY agrees upon evidence of fulfilled contract to render unto CONTRACTOR the following...)
Skills: Sense Motive, Knowledge: Arcana, Athletics
10+: The devil is requiring you to travel to an undisclosed location of "appropriate combative risk" to recover an item. The item is guaranteed to have no living owner.
15+: The item appears to be cursed, though not fatally. There is also no guarantee that the item doesn't have an undead owner.
20+: The area in question appears to be extremely dangerous for reasons other than local monsters. Some clauses mention obscure climbing terms that indicate only an expert athlete would be able to pass.