What LBS doesnt service road/race bikes???
As for the bike. I think £800 is a bit on the extreme end of the scale given its age. But it does tick the boxes as far as the drivetrain goes. but the brakes arent 105 they are Axis 1.0 which ive heard are absolutely terrible.
If the price was Between £600-650 it would be an absolute steal given the current climate. The price would need a fair knocking down before i would go for it but thats just me. I would be looking at upgrading the wheels and brakes pretty much instantly if i was to buy the bike so i would see how far i could push the price down. But your friend might not have the same qualms that i do with the bike so maybe he'll be happy just to be able to have a bike which is in reasonable condition even if he did pay well over the odds for it.
(The stock tyres are also on the heavy side so i'd be looking at switching those out too if it hasnt already been done! Fresh rubber!)
Just to put things into context a little more....
For an extra £50 - your friend could have a brand spanking new bike from decathlon (when they eventually have stock) and this bike will come with all the latest tech. 105 R7000 Drivetrain, TRP HY/RD Disc brakes -- which are absolute LEAGUES better than the Axis 1.0 which are some 6+ years old... and up to 2 years warranty on some parts (I think the frame is lifetime warranty)
Its not a carbon bike though, But if your friend really had to ask about the asking price of the SL4. I doubt he would have any issues with the RC520.