The problem of increasing price is no different than the problem of setting price. A model of assessment is required to reach a decision.
Typically, the first assessment is current and past performance.
You mentioned current pricing of $5.00 to $12.00.
What is your store’s average revenue per wash now and in the past? Is the average at, below or above the benchmark?
If below average, it may not be price but store and services design that requires attention because these factors are most linked to service quality and customer satisfaction. Conversely, if above average, you may be in a better position to raise price than you believe.
Is the average trending upward, downward or stable? If average is trending downward, increasing price may be risky.
You can also learn something about performance and price sensitivity by assessing store conversion rate. Conversion rate is sales dollars divided by traffic count.
For example, if store conversion rate is below the benchmark, it may not be price but customer
loyalty that needs attention.
Consequently, my advice is to assess performance then determine if there are any viable alternatives to increasing price.