Have been using CEX for years - both buying and trading in.
In store is always best as you can view your items before purchasing but online works great.
Recently bought a 265K Cpu and no issues, got for a good price as well.
My only issue with the online store is postage. If you buy say 5 Blu rays - they charge you €3.50 per item. This is because the physical shops send them so it’s not a true online repository.
Otherwise A+