To find the probability of randomly guessing the correct combination on a three-wheel combination lock, we first need to determine the total number of possible combinations.
Each wheel has 10 possible numbers (from 0 to 9), and since there are three wheels, the total number of combinations can be calculated as:
\[ 10 \text{ (numbers for the first wheel)} \times 10 \text{ (numbers for the second wheel)} \times 10 \text{ (numbers for the third wheel)} = 10^3 = 1000. \]
There is only one correct combination for the lock. Therefore, the probability of guessing the correct combination in one attempt is given by the ratio of the number of successful outcomes (1) to the total number of possible outcomes (1000):
\[ \text{Probability} = \frac{1}{1000}. \]
Thus, the probability that someone randomly guesses the correct combination in one attempt is
\[ \boxed{\frac{1}{1000}}. \]