The are several factors that help ensure a successful videoscan, and in my opinion the most important is proper lighting.
Normal photography just requires one side of the subject to be lit for a good 2D photograph. With 3D Selfies, the entire subject must be well lit 360 degrees at all sides and require special considerations.
Here are the two rules to follow to help ensure the best lighting for videoscans...
1) Indoor Lighting Only: Hard direct lighting and dark shadows are bad for videoscans, as such you need to perform the videoscan indoors under diffused yet well lit artificial lighting.
2) No Back-Lighting: Back lighting, such as a window or a lamp directly behind your subject, causes a glare that softens the edges of your subject and darkens the image making it difficult to convert your videoscan for 3D printing.
Before starting the videoscan, take a good look at your indoor surroundings. If in a home, a well-lit kitchen or garage is normally the best place to conduct the scan. Cover all windows in the room to avoid back-lighting.
The absolute best place to conduct videoscans are in department stores. They are packed with great overhead diffused lighting. Make sure to pick a day and time when they are not busy and ask if you can use their space to conduct the videoscan. You can perhaps offer them a free videoscan in trade, but be sure to charge them full price for their 3D Selfie.