Charge one price, or quote a range when it depends.
Most services have one price. Where the final figure depends on the client - length, condition, how much work it turns out to be - a service can show a range instead, and the booking page displays it as "from" the lower figure.
A range is a quote, not a charge. If you take payment online, the amount collected is the price you set for the booking, so use a fixed price where money changes hands up front.
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