A proof of shaving is sth basic. Every Sponsor can be accussed of shaving... It's very simple to create a thread on some Board... If you'll get somebody by the balls - post the proof - they'll have serious problems - that's for sure... We can suspect some things but... that's all actually...
If you don't like some Sponsor/Company and you think that they shave - just don't promote them - simple as that...
There's a lot of great Sponsors on the market nowadays so you can choose between them... Good luck !