i have over 200+ cels. and yes they real and different types. Many of them will be stock and will be marked as mu stk/ pp stk and should not cost more than $25. Remember filmation use 50% stock for each episode. if it includes a painted background, then it could be up to $100 but most backgrounds are stock that they have up for sale which won't be worth more than $30. Non stock cels will tell you the episode number such as mu 46/pp 01. Model cels are what the artist used as refence and never were filmed. Be care most are over price and has been up for sale for a long time. don't be scared to ask the sell for the numbers-- this will tell you if you can trust him and see if it an episode you want to collect from.
Hope this helps.