You're more than welcome to not purchase it
Shimano 105 group isn't average quality, not sure why you think that's the case as it is in the performance tier just before you step into the pro level.
The bike has been maintained with the chain regularly replaced and the cassette was also swapped out. The rear derailleur is currently an XT as I had a larger gearing setup for a while but I've got the original one laying around. I've also got an extra set of tires for the bike that I'll include and spare crankset if desired.