SOURCE: This comes from the Latin translation that accompanies De Furia's edition of the Greek Aesopic corpus, published in 1810 and available at GoogleBooks. This is fable 128 in De Furia; for other versions, see Perry 99.
READ OUT LOUD. Choose which marked text you prefer to practice with - macrons or accent marks - and read the text out loud until you feel comfortable and confident. Then, try reading the unmarked text at the bottom. It should be easy for you after practicing with the marked texts. :-)
MACRONS. Here is the text with macrons:
Cum quīdam Mercuriī simulācrum ex lignō fēcisset, ipsum vēnum proposuit. Sed cum nullus emptor accēderet, is emptōrēs alliciendī causā clāmāre coepit, aiēns sē Deum beneficum ac dīvitiārum datōrem vēnum dare. quīdam tunc ex iīs quī forte aderant, Ecquid, inquit, amīce, Deum tālem dīvendis, cum tūte ipse tot tantīsque eius beneficiīs fruī possīs? Cui ille, Egō quidem, ait, celerī subsidiō indigeō, hic autem tardē dīvitiās ferre solet.
ACCENT MARKS. Here is the text with accent marks, plus some color-coding for the words of three or more syllables (blue: penultimate stress; red: antepenultimate stress):
Cum quidam Mercúrii simulácrum ex ligno fecísset, ipsum venum propósuit. Sed cum nullus emptor accéderet, is emptóres alliciéndi causa clamáre coepit, aiens se Deum benéficum ac divitiárum datórem venum dare. quidam tunc ex iis qui forte áderant, Ecquid, inquit, amíce, Deum talem divéndis, cum tute ipse tot tantísque eius benefíciis frui possis? Cui ille, Ego quidem, ait, céleri subsídio indígeo, hic autem tarde divítias ferre solet.
UNMARKED TEXT. Here is the unmarked text - after practicing with the marked text that you prefer, you should not have any trouble with the unmarked text:
Cum quidam Mercurii simulacrum ex ligno fecisset, ipsum venum proposuit. Sed cum nullus emptor accederet, is emptores alliciendi causa clamare coepit, aiens se Deum beneficum ac divitiarum datorem venum dare. quidam tunc ex iis qui forte aderant, Ecquid, inquit, amice, Deum talem divendis, cum tute ipse tot tantisque eius beneficiis frui possis? Cui ille, Ego quidem, ait, celeri subsidio indigeo, hic autem tarde divitias ferre solet.
IMAGE. Here is an illustration for the story (image source) showing an ancient herm!