At #bicyclecouriers we send all types of bicycles, including road bicycles, race bikes, tri-bikes (triathlon), MTB mountain bikes, gravel bikes, kids bikes, balance bikes, first-time bikes, single-speed bicycles, commuter bicycles and more -- as long as it fits into a 'standard bike box'. And this is where there are notable exceptions: fat bikes and e-bikes and tandems.
Because of the size of the latter, they may need to be transported in TWO standard bike boxes, effectively incurring double the cost of a normal bike transfer. I've send a 20" kids fat bike in a standard box without any problems, but on the other end of the spectrum also dealt with an e-fatbike, a double whammy  that filled two boxes because of the sheer size of the thing. So there you have it: standard box, standard price. Two boxes, double the rate.