Could be blight or maybe leaf spot. Both are treatable, if not curable, with a copper sulfate spray or a weak solution of hydrogen peroxide. But it could also be fusarium or verticillium wilt, in which case the prognosis is poor. The gardener should have used a disease - resistant variety. You have to face it.
Pests are the order of the day with tomatoes.
Expect leaf damage, but don't let it drive you crazy. Some insects, such as leafminer, will make the leaves look awful, but they will not affect fruit yields. One of the reasons we grow our own food is to have some control over what chemicals go on it. It's best to avoid heavy doses of pesticides. Use commercial insecticidal sprays as a last resort.