An in-game solution would be to use Divination spells to narrow down the difficulty level.
I see that most other answers are not answering your actual question, and instead are offering contrary advice.
A common factor in many systems of spells with Divinations is the Twenty Questions concept. You ask a question, you get a Yes, No, or Unknown types of answers, maybe with a short comment; and you only get so many questions per casting. Higher level divination spells typically yield more detailed results.
Having a database of known variables (ie: people on tap of various skill levels and known accomplishments) to compare the answers to can allow a company (or guild, club, religion, government, and so forth) to roughly estimate just how challenging a particular quest would be, without actually being too specific or exactly right: sort of like predicting the weather. You ask if so-and-so could finish the task, and work your way up the variously rated people until you get a 'yes' response.
Repeat this question and answer process with a number of different skill sets, and you will get a profile of who could accomplish this task with what skills. Cross index by the history of missions these people have accomplished, or even ask another set of questions about if this quest will be more difficult than other quests on record. Once all this information is gathered, then a good estimation of Quest Difficulty can be made.
This process leverages the capabilities and resources of a large organization to accomplish a fairly large amount of information gathering in a short amount of time, something which a typical individual could not accomplish on their own.
An example of using divination spells to determine challenge level is given as follows. This particular example is set in a guild, but a similar board (or even multiple boards) could exist in nearly any village, town, city, school, church, and so forth:
Galrand the Sorcerer Grenlick (he's a "professional locksmith" and his name is actually Steve, but that's how nicknames go sometimes), showed up to work one day only to find a stack of new re-Quests in his inbox to sort for the Bounty Board. He groaned. He hated the drudgery of trying to assign appropriate ratings to those things. Steve walked over to his boss's cubicle to complain, only to realize that this was his week off. The cheerful note on the magically bright-yellow square of parchment only hammered the point home. "Thinking of you, Galrand, while I'm on vacation!"
Steve fumed and cursed his boss internally. That black-hearted half-pint, smelly poisonous toadstool... nice and kind and totally handsome boss; Steve quickly amended his thoughts as Xiao-Wu the Mentalist wandered past with a stack of packages, and gave him a look in passing. She was really cute, but great and little godlings did the whole mentalism thing put one off. He smiled wanly as she suddenly paused, looked back, and threw him a wink and saucy smile.
Steve sluffed off for a bit at the water cooler to recover, before he finally wandered down to the Guild pool to see which diviners are currently available. He hid in the shadows to avoid being spotted, pointedly ignoring the posted notices above his head of "Nextly come, nextly served. No skipping!" and Equal Opportunites, Equally shared..
Steve muffled his snickers as Bob from the Prospecting Division fell prey to Grunhilda the Orcish Prognosticator who was the next diviner who became available. He had never liked that snob anyway, and Grunhida's divination methods tended to be... painful. And bloody.
Seeing that Aliannashia the super-hot-elven-priestess-of-some-super-hot-elven-goddess-that-he-can-never-remember-her-name-of was just finishing up with some nobody, Steve slicked back his hair, scooted into line, and sucked in his belly a bit.
Seeing him, she rolled her eyes at his toothy grin, and waved him over with a sigh. "I don't need to cast a divination to know that you aren't getting a date with me, Galrond."
"Hey, don't knock it until you've tried it." Steve replied with a 'hurt' tone. "And it's Galrand."
"Whatever." She rubbed her slender fingers against her temples as if warding off a headache. "Why are you here this time?" she asked with a resigned tone.
Steve presented the stack of re-Quest forms to her with another grin. "Official business!" he chirped smugly. She somehow managed to get them out of his hands without touching him, a real trick considering his manual dexterity.
"Woohoo. Lucky me. Come on, then." She gracefully trudged back to her desk, while Steve followed, appreciated the view, and idly wondered how trudging gracefully even worked. Once settled she took the first of the stack and set it in the gem encrusted miniature magic circle chiseled into her desk. After some mumbo-jumbo nonsensical sounds and graceful (of course) passes and waves of her hands, the parchment floated slightly and her voice changed subtly, "SPEAK. ASK."
Steve stuck strictly to business, and asked the recommended series of questions: 'if so-and-so performed this quest, would they see success' working his way up the chain of increasingly skilled guild adventurers until he received a "YES" response. Then he recorded down the name and officially-estimated rating level of the re-Quest based on the Guild's extensive workup of each person's abilities. For tricky re-Quests, he had to try people with obscure and rare skill sets before he received a divinely inspired "YES". Aliannashia changed the papers mechanically as he handed them to her. Finally, he snuck in his usual, "Will I get a date with Aliannashia?"
There was a pause. He glanced up to check if she was still in the magical trance, and was shocked when he saw actual eyes looking back at him... but not her eyes. "WE REMEMBER YOU. YOU'RE PERSISTENT. THIS IS THE 71ST TIME YOU'VE ASKED THAT. SHOW UP TO A FEW OF MY SERVICES AND WE WILL CONSIDER TO HAVE A WORD WITH HER."
Steve gaped in shock for what seemed forever, before he managed to force out in a whisper, "Yes, Ma'am," gathered up the stack of parchments and fled.
After he recovered, and checked his appearance in the washroom mirror, he stamped the re-Quests with the appropriate color and number of stars; then headed into the common room to post them all on the Bounty Board, while he internally debated with himself if getting a date with Aliannashia was worth suffering through some sermons.