I'm very sceptical about their claims.

You're wrong. I'm not pessimistic, but sceptical.

News of the company's expansion plans was greeted with scepticism by the local community.

The majority of mankind is lazy-minded, incurious, absorbed in vanities, and tepid in emotion, and is therefore incapable of either much doubt or much faith; and when the ordinary man calls himself a sceptic or an unbeliever, that is ordinarily a simple pose, cloaking a disinclination to think anything out to a conclusion.

Dr Tyler expressed scepticism at Dr Ramsay's revolutionary new therapy.

They are sceptical of all the newcomers.

The scepticism is not entirely unwarranted: many journalists have warned that the government is not being entirely truthful.

Tom seemed sceptical.