Laudator Temporis Acti

Seneca, Agamemnon 56-64, in John G. Fitch, ed. and tr., Seneca, Oedipus, Agammemnon, Thyestes. [Seneca,] Hercules on Oeta, Octavia (Cambridge: Harvard University Press, 2004 = Loeb Classical Library, 78), pp. 130-131:

O regnorum
magnis fallax Fortuna bonis,
in praecipiti dubioque locas
excelsa nimis.
numquam placidam sceptra quietem        60
certumve sui tenuere diem;
alia ex aliis cura fatigat
vexatque animos nova tempestas.

O Fortune, beguiler
by means of the great blessings of thrones,
you set the exalted
in a sheer, unstable place.
Never do sceptres attain calm peace
or a day that is certain of itself.
They are wearied by care upon care,
their spirits tossed by some new storm.

I don't think bonis (line 57) is ablative of means, as Fitch's translation implies, or even ablative at all, but rather dative. See R.J. Tarrant, Seneca, Agamemnon. Edited with a Commentary (1976; rpt. Cambridge: Cambridge University Press, 2004), p. 184:

Fortuna is deceitful toward the riches that accompany rule; for the dative compare Pliny, N.H. 3.80 nauigiis fallax, Tac. Hist. 1.22 potentibus infidum, sperantibus fallax...

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Thanks to Eric Thomson for drawing my attention to Fitch's Annaeana Tragica: Notes on the Text of Seneca's Tragedies (Leiden: Brill, 2004), p. 156 (on Agamemnon, line 57):

Is magnis bonis dative or instrumental ablative? I incline to the latter alternative for two reasons. First, Fortune does not deceive the wealth and power of kings, but rather deceives humans who are taken in by such things, regarding them as secure or as true bona. Second, magnis bonis must be ironic here, and the irony is more evident if the idea of 'blessings' is closely linked with that of deception. (There is then no need to consider Axelson's vanis for magnis.) For fallax with an ablative cf. Pliny NQ 25.8 pictura fallax est coloribus tam numerosis, Tac. Ann. 16.32 specie . . . amicitiae fallaces (the first causal rather than instrumental, but with much the same effect).

For "Pliny NQ" read "Pliny NH".