You generally don't want flavorings that are/contain oil. Supermarket flavorings are usually a risk, but I've done it. Make sure they contain PG and flavoring (without oil), and nothing else.
You're best off ordering from wizardlabs.us, highdesertvapes, ecigxpress, onestopdiyshop, etc. Flavoring is much cheaper online too. Wizard has 8ml vials for $1.50 right now.