Are Sellers required to use Redline Shipping?

Not at all. There are other legitimate third-party shippers that specialize in shipping reptiles, amphibians, and invertebrates. And sellers may have their own personal accounts with FedEx or UPS*. 

MorphMarket has partnered with Redline Shipping and recommends them because we think they are a great service. Robyn Markland and the Redline team draw on decades of experience to provide excellent online experience, highly competitive rates, and customer support. But we do not require that any of our sellers use them instead of other legitimate alternatives.

*Most reptile shippers use FedEx, but UPS also allows some live animal shipping. Those specializing in lizards or amphibians, for example, may choose to use UPS. UPS does not allow the shipping of snakes, although when they made that rule they did grandfather in exceptions for a few of their biggest customers. So far as we're aware, there are no legitimate third-party shippers for reptiles through UPS.