Don't you all have a "Rating"? Then at least you know what your opponent is all about. Here's a breakdown of the USTA Tennis Rating System ...
USTA TENNIS RATING PROGRAM
This player still lacks stroke dependability, depth and variety but has improved ability to direct shots away from opponent; rarely double faults but does not usually force errors on the serve; hits forehand and backhand volleys consistently; and has often played for several years.
This player has dependable strokes on both forehand and backhand sides; has the ability to use a variety of shots including lobs, overheads, approach shots and volleys; can place the first serve and force some errors; is rarely out of position in a doubles game; plays tournaments and is good enough to compete at the higher positions on most high school teams.
On that, I think, on a good day I'm a 4.0 and on a bad day a 3.5.