This is a source of many mistakes (would be much less so if people did not submit observations of planted trees). Here are a coupe of things to look out for:
with flowers: the first thing one should look at (or take a picture of) with this kind of blossoms (but almost nobody does) is look at the backside of the flower. In Prunus avium the sepals are very soon reflexed, the hypanthium is cupshaped (or bowlshaped if you like) with an obvious constriction at the top (this constriction is not visible anymore as soon as the petals are reflexed) and glabrous. The pedicels are glabrous too and the inflorescence never has a central stalk. In ornamental cherries, sepals are not reflexed and there are always others things that do not fit: E.g sepals strongly triangular, hypanthium or pedicels hairy, hypanthium narrowly cylindrical, inflorescense compound with central stalk etc. etc…
2.Without flowers but with leaves: Although highly variable, the leaf serration in Prunus avium is characteristic: rather blunt and in part unequal leaf teeth (a bit sloppy looking). There are many pictures of P. avium on inaturalist.org . Use them to get a little practice or for comparison. In ornamental cherries, the leaf serration always looks very different (in many possible ways, depending on the species/hybrid).
3. No flowers, no leaves: let it be.
There are numerous ornamental cherries (belonging to various species and their hybrids). Exactly ID’ing them is a job for a specialist (and if you found an escaped ornamental cherry, it could even be a hybrid of different horticulture varieties), so be careful.