Coulomb excitation is a standard method used to extract quadrupole excitation strengths of even–even nuclei. In typical analyzes the reaction is assumed to be one step, Coulomb only, and is treated within a semi-classical model. In this work, fully quantal coupled-channel calculations are performed for three test cases in order to determine the importance of multi-step effects, nuclear contributions, feeding from other states and corrections to the semi-classical approximation. We study the excitation of $^{30}$S, $^{58}$Ni and $^{78}$Kr on $^{197}$Au at ≈50 A MeV. We find that nuclear effects may contribute more than 10% and that feeding contributions can be larger than 15%. These corrections do not alter significantly the published B(E2) values; however, an additional theoretical error of up to 13% should be added to the experimental uncertainty if the semi-classical model is used. This theoretical error is reduced to less than 7% when performing a quantal coupled-channel analysis.