If you google DDG Axis XC and investigate it then you'd find that you could probably make more selling the individual parts. The chances are if you tried to ebay your complete bike wouldn't make £100 but you have fees, packaging, time and hassle to take into account. I'd let Evans have it.
It works on a you buy a bike of X value and we will give you y value off when you give us your old bike.
The value of the bike I'm buying is giving me £100 off.