With the S&P 500 chalking up a five-year high on Tuesday, it probably comes as no surprise that nearly 55% companies in the Motley Fool CAPS database are within 10% of a new 52-week high. For skeptics like me, that's an opportunity to see whether companies have earned their current valuations.

Keep in mind that some companies deserve their current valuations. Fertilizer products maker Agrium (NYSE: AGU), for instance, recently boosted its upcoming quarterly EPS guidance to more than $2 from a previous range of $1.50 to $1.90. Agrium cited better-than-expected grain and oilseed pricing for boosting demand, but I believe it speaks to a longer-term trend of placing more emphasis on utilizing fertilizers to improve crop yield for a growing world population.

Still, other companies might deserve a kick in the pants. Here's a look at three companies that could be worth selling.

Run away... run away!
To quote King Arthur in Monty Python & the Holy Grail, "Run away... run away!"

I'll admit that I'm as stunned as anyone that Keryx Biopharmaceuticals' (KERX) kidney disease drug Zerenex performed so well in trials. Zerenex, designed to treat hyperphosphatemia, a complication often arising in end-stage renal disease, reduced serum phosphorus levels by 0.3 mg/dL during a four-week efficacy period while patients on the control arm saw their serum phosphorus levels rise 1.9 mg/dL. Without question, drug efficacy has been demonstrated by this trial. But can Keryx effectively market the drug? That's an issue I'm very uncertain about.

Keryx responded to its positive results by diluting shareholders with a $55 million offering, but it will almost certainly need to find a commercial partner for Zerenex if it has any hope of effectively marketing the drug. That partner will ultimately take its cut and leave Keryx on the borderline of profitability at best in a few years. It is worth mentioning that Keryx does have a partner in Japan, JT & Torri, but beyond that, I don't see how it succeeds in the U.S. without a commercial partner.

Beyond Zerenex, Keryx has absolutely nothing in its pipeline.Keryx's share price was crushed last year when Aeterna Zentaris reported that cancer drug perifosine had failed to meet its primary endpoint in a multiple myeloma study. Perifosine had been licensed to Keryx within the United States, Canada, and Mexico by Aeterna Zentaris. Had Zerenex failed in trials, Keryx would be sitting on its hands with an empty pipeline.

With plenty of questions yet to be answered, I'm staying away from this killer rabbit!

Something smells fishy
Normally, health and beauty products tend to survive economic slowdowns pretty well, but the valuation on fragrance maker Inter Parfums (IPAR 3.20%) is beginning to smell like a rotten egg.

Inter Parfums' entire business structure is to enter into long-term contracts with well-known luxury brand names and manufacture and distribute fragrances for those companies. It currently boasts a portfolio with high-end names like Jimmy Choo and Montblanc. Unfortunately, in June Burberry made it clear that it wanted to terminate its agreement with Inter Parfums and develop its own fragrance. The termination netted Inter Parfums a hefty $236 million pre-tax payment, but leaves its sales severely lacking in the growth side of its business in the coming year, in spite of a newly signed 10-year agreement with Alfred Dunhill.

Another factor that makes me want to steer clear of Inter Parfums is its overreliance on Europe. According to its annual report, 87.4% of all sales were derived from Europe. In the fourth quarter, its Europe sales actually fell 10% as widespread austerity measures are beginning to cut spending throughout the entire region. Inter Parfums is doing what it can to expand into the U.S., but as the country represents just one-eighth of its sales, it's going to need Europe to turn around if it expects any organic growth.

Based on the midpoint of its newly issued EPS guidance ($0.91), Inter Parfums is valued at 24 times 2013's earnings -- a very steep price to pay for a company so intricately tied to Europe and that just lost Burberry as a customer.

Reality called, it wants you back
Shareholders of residential and commercial building products supplier Nortek (NASDAQ: NTK): Reality called and said it wants you to wake up from fantasyland!

Nortek, a maker of kitchen range hoods and exhaust fans, has benefited from a resurging housing market where home prices have begun to creep higher and inventories have fallen dramatically. However, Nortek's share price has nearly tripled over the past year despite its bottom line being anything but robust.

A quick look at its latest quarterly filing reveals a 1% year-over-year increase in third-quarter sales to $557.4 million, a 260-basis-point improvement in gross margin to 28.4%, and its fourth consecutive quarter of positive free cash flow. Again, this is a step in the right direction, but on a trailing-12-month basis, Nortek is now valued at 53 times earnings. For that sort of P/E I'd better be investing in a high-growth or high-technology type of company, not one that produces range hoods and exhaust fans.

With only four quarters of positive free cash flow under its belt and an astronomical trailing P/E, I'm going to need to see much stronger growth before I'd even give it a remote chance of heading higher from here.

Foolish roundup
This week's theme is all about stepping back from the ledge. Keryx, Inter Parfums, and Nortek all have serious questions to answer with their recent share price appreciation. Keryx's marketing of Zerenex, Inter Parfums' loss of Burberry, and Nortek's few avenues of growth are clear concerns that could merit some attention from short-sellers.

I'm so confident in my three calls that I plan to make a CAPScall of underperform on each one. The question is: Would you do the same?