Is that true or is it an FF myth? I had a swatch at their fairly recent transfers. They most certainly did not get top dollar for Van Dijk who moved on for an enormous amount a couple of years after he let them for Southampton.In fairness they do get absolute top dollar fees for their players. Something that we need to improve on.
Forster at £10m and Armstrong at £7m seems about right for 'ordinary' EPL players (we paid I think £7m for Kent who couldn't get near Liverpool's first team and Solanke, another Liverpool reserve, went for £20m). Dembele seemed generous at £20m or whatever but he held a place last season in the French top division and is now heavily rumoured to be moving to Atletico. That doesn't seem an extraordinary price.
Tierney is the outlier, £25m does beggar belief but he does not lack talent especially going forward and was outstanding in an Arsenal game I saw recently. If he comes good (and manages to actually play given his injury history) £25m will not seem excessive.
Sviatchenko went for £1m while Boyata, Sinclair and a fair few lesser players left for nothing.
Only Tierney and maybe Dembele seem to be over the odds or top dollar.