Lidl riberac

I am a little concerned having experienced Lidl in Riberac for several years. Two years ago when I was going through a slight financial crisis I went to Lidl - proffered a 20€ note and was given change for 10€ - I queried this and the assistant sighed loudly and called someone from the office to take away the till and check it - I was proved correct - I knew - and was given the appropriate change. Since that time I have watched carefully - and recently experienced something similar - I noticed that the checkout was littered with till receipts - the same assistant now does not give your receipt unless you ask for it! - I have warned several friends who also expressed doubts about this particular assistant - there are only two - the other one is lovely - what to do? - if this woman makes 10€ from 10 customers per day - it is a substantial sum - and I know from experience that men do not check their change or ask for a till receipt - anyone else experienced anything similar?