There is two issues here:
1. Is the VIC model reliable for your location
2. The client does not trust the VIC model but does trust the result of the other two models.
It is hard to say if the VIC model is reliable but an analyses by Roudier et al. (2016) judged that all three models have sufficient performance to be included in the flood analyses. Our analyses in Roudier et al. also showed that Lisflood showed historically the best performance. This is not surprising given this model is developed specifically for floods in Europe. If we look at the future, the European patterns for the future are relatively similar for all three models in terms of predicting more floods throughout central Europe (see figure S3 in Roudier et al. 2016). So what you are finding is probably specific for your site. In general all three models give increases in in 1/10 and 1/100 year floods throughout most of Europe. So the VIC models could be non reliable but the conclusion that because the model gives a different result it should be discarded is not valid. However the larger scale pattern is different (more floods) and the fact that the other two models do show increases makes it likely that floods will increase and raises some question about the VIC results. The main differences of VIC compared to E-Hype and LisFlood are in how the models estimate snowmelt. If the increase in floods in E-Hype and Lisflood are mainly in spring due to earlier snow melt this could explain the difference between the models.
It is important to add a note here on HBV: this is a good model for floods under current conditions and some flood monitoring but has some limitations for climate change impact assessments. Due to the simple snow melt routine and the way it estimated evaporation.
A second important point is the trust of the client. Your client indicates that he trusts the other two models more. This is a concern you need to take serious. Given that one models gives a different results, the overall trends across multiple assessments indicate more floods in central Europe and the fact that your client trust the other two models I would recommend to do analyses with E-Hype and Lisflood only.
Let me know if you any additional questions
send me an email (firstname.lastname@example.org) if can’t access the paper and I will send you a copy.
Roudier, R., J.C.M. Andersson, C. Donnelly, L. Feyen, W. Greuell & F. Ludwig 2016. Projections of future floods and hydrological droughts in Europe under a +2°C global warming, Climatic Change 135, 341-355
link to paper: https://link.springer.com/article/10.1007/s10584-015-1570-4