If the researcher has not produced anything after a year, they will find it difficult to obtain any grants after that, because recent publications are a factor in grant decisions. It would be a great way to stall your career. So researchers tend to try pretty hard to produce something once they receive a grant. Also, there's not that many sources of funding out there, so if you totally waste an agency's grant they might remember it when you apply to them again.
Some grants restrict what they may be used for. You cannot, for example, apply for a grant saying you will research X and then instead research a completely different topic Y. Everything you purchase or pay for with the grant money has to be tabulated and reported to the funding agency. If there's stuff that is obviously not related to the research, there may be various repercussions. It depends on the agency how closely they look at your expenses and how strict they are about judging them.
There are also some grants that are structured in installments. You don't get the whole money right away. You have to meet with the agency's officials periodically (for example yearly or every 6 months) and give them an update on your progress. If they don't like the update, you might not get the rest of the money.
Lastly, there is not necessarily an expectation that results must be produced. Science deals with the unknown, so it's inevitable that sometimes the hypothesis just turns out to be wrong. So many funders take broader view. They accept that there will always be some studies that fail, and it's not necessarily the researcher's fault. At the proposal stage, they try to pick applications that would still produce some useful results even if they failed.
The problem is that some professors are not active at all, they offer really low quality courses, they use the same material, same assignments, etc.
Research grants don't really care about the quality of your courses. They are primarily concerned with research. There are sometimes specialized grants that do also take teaching/outreach into account, and these will of course expect you to provide evidence that your courses are high quality.