GPS Verifier uses your phone's location services to find your location. These can be disabled (in which case you should get an immediate error), or they can be set to use a lower accuracy method of geolocation. There are three methods of getting a location on a mobile device:
1. GPS, which uses satellites to find your location (want to know where the satellites are right now? Check out [in-the-sky.org]). GPS is highly accurate, but your ability to get a GPS signal can be affected by many factors. These include blockage by buildings (called the "urban canyon" phenomenon) or natural features such as mountains or hills, weather/cloud cover, "space weather" (electromagnetic disturbances beyond the earth's atmosphere), and nearby radio emissions.
2. Cellular signal location, which uses signals from one or more cell towers to find your location. This is very fast, but also the least accurate method of finding a location.
3. Wifi hotspot. This uses a method called "IP location" which can be quite accurate, or very far off (most likely in rural areas).
When GPS Verifier asks your phone for a location, the phone's operating system (Android or iOS) tries to get a location using one of the methods above -- usually the quickest one available. If it can't get one, you'll see a "can't get location" error in GPS Verifier (note that this can happen even if you're able to get a location using Google maps or something like that, because there's a timeout in GPS Verifier -- after a while, it assumes you just don't have a signal). If your phone gets a location, it sends the location plus the accuracy to GPS Verifier. At that point, GPS Verifier has to make a judgment call as to whether the accuracy is good enough. If it isn't, you'll see a "can't get accurate location" error message.
WHAT CAN YOU DO ABOUT IT:
1. If you're using an Android device running version 4.4 or later, you can set your location mode to high accuracy.
2. Try to get your code while outside a building, with an unobstructed view of the sky. Note that at any given time, your view of a satellite may be low on the horizon, not directly overhead. People who live in hilly areas (like me!) just have a harder time of it with GPS.
3. If you're connected to a wifi network, try turning off wifi to see if you can get a more accurate location.
WHAT HAPPENS IF SASSIE THINKS MY LOCATION IS WRONG?
If you got a GPS Verifier code, and the map shows you exactly where you should be, don't worry -- the problem is probably with the location in SASSIE. When your GPS Verifier code is entered in SASSIE, it's compared to the location as entered in SASSIE. If the location in SASSIE is off (for example, error in the zip code) or was incorrectly geolocated, there will be an error message. Simply explain the situation to the scheduler (don't worry about sending them the map, they can see the location of your GPS Verifier code when they review the shop), and if you really want to go the extra mile, provide an additional link (for example, from Google maps) that shows the business location.