They look like Sora 8 speed shifters ok but my rear derailleur didnt look like that...is it Sora ?
Circa £100 ?...pay close attention to the following...
Spin the wheels...are they true and no wobbles. Is there any graunchiness about them, do they spin well. Finger and thumb round the tyres at the top and feel for sideways play in the hub. If everything is smooth an no play...great.
A quick ride, do the gears all shift cleanly, click through each one as you ride.
Pay attention to the crankset as you ride it...any graunchiness. ?
Close look at the chainrings...sharks teeth indicate theyre worn. If you're not sure, pay close attention to the other one and compare the profiles.
Flip the frame over and have a close look at the welds, particually round the BB, look for any cracks.
Sounds a lot to take in, but you can do all that in 5 minutes.
If it all works ok, £100 ish seems ok.