The ratings of three Service stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Mac-Gray (NYSE:TUC) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Mac-Gray supplies card and coin-operated laundry services in multiple housing facilities. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum, Earnings Surprise, and Margin Growth, TUC also gets F’s. The stock price has fallen 12.5% over the past month, worse than the 3.5% increase the S&P 500 has seen over the same period of time. The stock’s trailing PE Ratio is 458. To get an in-depth look at TUC, get Portfolio Grader’s complete analysis of TUC stock.

Collectors Universe (NASDAQ:CLCT) gets weaker ratings this week as last week’s C drops to a D. Collectors Universe provides third-party authentication, grading, and related services for rare and collectible items. The stock also gets an F in Margin Growth. For more information, get Portfolio Grader’s complete analysis of CLCT stock.

Ambow Education (NYSE:AMBO) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). Ambow Education is a national provider of educational and career enhancement services in China. In Earnings Growth, Earnings Momentum, Earnings Revisions, and Margin Growth the stock gets F’s. For a full analysis of AMBO stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.