Context: because in satire the poet focuses attention of the failings of men, and because there are so many failings, there is much room for satire. The quotation is one example, the merchant.
hic mutat merces surgente a sole ad eum, quo
vespertina tepet regio, quin per mala praeceps
fertur uti pulvis collectus turbine, nequid
summa deperdat metuens aut ampliet ut rem.
Translation:
This man trades goods from from eastern climes with him, from where
in the western region things warm up, even headlong he’s
borne like dust in a whirlwind, dreading
to lose capital, or wishing [ut] to add to it.
Here are my readings of which I’m uncertain:
ad eum: to the man with who goods are traded
vespertina: adjective, feminine, ablative, modifying regio
tepet: interpreted impersonally
ampliet ut rem: ut after a verb of fearing “implies a wish contrary to the fear”, Lewis & Short, “ut”. On the one had he fears that he will lose from his capital, and on the other he wishes he might add to it.
And I do urge you to learn to read the lines metrically, as hexameters. The meter is not that hard to get a handle on, and to ignore the fact that Horace is composing verse is well-nigh perverse. Quite apart from its helpfulness: vespertina could not be ablative.
This is the Satire that begins Eupolis atque Cratinus Aristophanesque poetae, isn’t it? An unforgettable first line, and a great mnemonic for the three most important comic poets of classical Athens. Horace may disclaim the status of a “poet” in the Satires, but he does write verse.