I think that the selection of "Not Available" needs to either be expanded or more completely verified.
Here in the US many to most gas stations will list the price for regular unleaded and diesel on their big signs. I think that a lot of people are driving around entering prices as they drive by (dangerous, covered already), and entering "N/A" because they don't know the price of mid-grade and premium. As I understand it, this defeats the purpose of being able to enter your preferred fuel type and searching for it as you're driving.
I have some suggestions for fixing it:
1) Add an additional pop-up question when somebody selects "N/A" for a fuel price - "Does this station NOT CARRY this grade of fuel, or do you NOT KNOW the price for this grade?" with appropriate buttons to select. That way, drive byes could select NOT KNOW, leaving the old price.
2) Add an additional button saying "UNKNOWN" instead of just the "NOT AVAILABLE" button.
3) Only allow fuel price entry if the current speed is < 1MPH. This will completely eliminate the drive by entries, and people should be able to enter the price of all grades while standing by the pump.
4) Possibly combine 1 & 2. Always ask the question if someone selects "Not Available".
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