Well the most commonly sold bichir is a senegal. They are very active and can have a creamy or light gray appearance. They are one of the smaller bichirs averaging about 10in.
They are also upper jaw protruding and have a patternless body. Although when they are young they will have a couple lines going horizontally across their body which will fade with age
Price can be another clue if they are $5-7.00 they will be senegalsbut in general senegals have no pattern all other species have a clearly defined patterns at early ages-Anne
In addition to being plain-jane they'll have a different dorsal ray count the most others. another plain one is the palmus. Of the 2 the senagal has been dorsal rays.