From the Suda

“To speak Cretan to Cretans: Since they liars and deceivers”

Κρητίζειν πρὸς Κρῆτας. ἐπειδὴ ψεῦσται καὶ ἀπατεῶνές εἰσι.

Hesychius

“krêtizein: used for lying and deceiving. People use this phrase because Krêtans are liars.”

κρητίζειν· ἐπὶ τοῦ ψεύδεσθαι καὶ ἀπατᾶν. ἔταττον δὲ τὴν λέξιν ἀπὸ <τοῦ> τοὺς Κρῆτας ψεύστας εἶναι

Zenobius, 4.62.10

“To be a Cretan: People use this phrase to mean lying and cheating. And they say it developed as a proverb from Idomeneus the Cretan. For, as the story goes, when there was a disagreement developed about the greater [share] among the Greeks at troy and everyone was eager to acquire the heaped up bronze for themselves, they made Idomeneus the judge. Once he took open pledges from them that they would adhere to the judgments he would make, he put himself in from of all the rest! For this reason, it is called Krêtening.”

Κρητίζειν: ἐπὶ τοῦ ψεύδεσθαι καὶ ἀπατᾶν ἔταττον τὴν λέξιν, καὶ φασὶν ἀπὸ τοῦ ᾿Ιδομενέως τοῦ Κρητὸς τὴν παροιμίαν διαδοθῆναι. Λέγεται γὰρ διαφορᾶς ποτὲγενομένης τοῖς ἐν Τροίᾳ ῞Ελλησιν περὶ τοῦ μείζονος, καὶ  πάντων προθυμουμένων τὸν συναχθέντα χαλκὸν ἐκ τῶν λαφύρων πρὸς ἑαυτοὺς ἀποφέρεσθαι, γενόμενον κριτὴν τὸν ᾿Ιδομενέα, καὶ λαβόντα παρ’ αὐτῶν τὰς ἐνδεχομένας πίστεις ἐφ’ ᾧ κατακολουθῆσαι τοῖς κριθησομένοις, ἀντὶ πάντων τῶν ἀριστέων ἑαυτὸν προτάξαι. Διὸ λέγεσθαι τὸ Κρητίζειν.

Dionysius Attic, Aelian

“Krêtizein: to lie. For Idomenus, when he was placed in charge of distributing the bronze from the spoils, chose the best for himself.”

κρητίζειν· τὸ ψεύδεσθαι. ᾿Ιδομενεὺς γὰρ ἐπιτραπεὶς τὸν ἀπὸ τῶν λαφύρων χαλκὸν διανεῖμαι τὸν ἄριστον αὑτῷ ἐξείλετο.

There is another tradition too for why Cretans are liars:

Medeia’s Beauty Contest: Fr. Gr. Hist (=Müller 4.10.1) Athenodorus of Eretria

“In the eighth book of his Notes, Athenodorus says that Thetis and Medeia competed over beauty in Thessaly and made Idomeneus the judge—he gave the victory to Thetis. Medeia, enraged, said that Kretans are always liars and she cursed him, that he would never speak the truth just has he had [failed to] in the judgment. And this is the reason that people say they believe that Kretans are liars. Athenodorus adds that Antiokhos records this in the second book of his Urban Legends.”

Ἀθηνόδωρος ἐν ὀγδόῳ Ὑπομνημάτων φησὶ Θέτιν καὶ Μήδειαν ἐρίσαι περὶ κάλλους ἐν Θεσσαλίᾳ, καὶ κριτὴν γενέσθαι Ἰδομενέα, καὶ προσνεῖμαι Θέτιδι τὴν νίκην. Μήδειαν δ ̓ ὀργισθεῖσαν εἰπεῖν· Κρῆτες ἀεὶ ψευσταὶ, καὶ ἐπαράσασθαι αὐτῷ, μηδέποτε ἀλήθειαν εἰπεῖν, ὥσπερ ἐπὶ τῆς κρίσεως ἐποίησε. Καὶ ἐκ τούτου φησὶ τοὺς Κρῆτας ψεύστας νομισθῆναι· παρατίθεται δὲ τοῦτο ἱστοροῦντα ὁ Ἀθηνόδωρος Ἀντίοχον ἐν δευτέρῳ τῶν Κατὰ πόλιν μυθικῶν.

Of course, in the Odyssey Idomeneus shows up in Odysseus’ lies

Od. 13.256-273

“I heard of Ithaca even in broad Krete
Far over the sea. And now I myself have come
With these possessions. I left as much still with my children
When I fled, because I killed the dear son of Idomeneus,
Swift-footed Orsilokhos who surpassed all the grain-fed men
In broad Krete with his swift feet
Because he wanted to deprive me of all the booty
From Troy, over which I had suffered much grief in my heart,
Testing myself against warlike men and the grievous waves.
All because I was not showing his father favor as an attendant
In the land of the Trojans, but I was leading different companions.
I struck him with a bronze-pointed spear as he returned
From the field, after I set an ambush near the road with a companion.
Dark night covered the sky and no human beings
Took note of us, I got away with depriving him of life.
But after I killed him with the sharp bronze,
I went to a ship of the haughty Phoenicians
And I begged them and gave them heart-melting payment.”

“πυνθανόμην ᾿Ιθάκης γε καὶ ἐν Κρήτῃ εὐρείῃ,
τηλοῦ ὑπὲρ πόντου· νῦν δ’ εἰλήλουθα καὶ αὐτὸς
χρήμασι σὺν τοίσδεσσι· λιπὼν δ’ ἔτι παισὶ τοσαῦτα
φεύγω, ἐπεὶ φίλον υἷα κατέκτανον ᾿Ιδομενῆος,
᾿Ορσίλοχον πόδας ὠκύν, ὃς ἐν Κρήτῃ εὐρείῃ
ἀνέρας ἀλφηστὰς νίκα ταχέεσσι πόδεσσιν,
οὕνεκά με στερέσαι τῆς ληΐδος ἤθελε πάσης
Τρωϊάδος, τῆς εἵνεκ’ ἐγὼ πάθον ἄλγεα θυμῷ,
ἀνδρῶν τε πτολέμους ἀλεγεινά τε κύματα πείρων,
οὕνεκ’ ἄρ’ οὐχ ᾧ πατρὶ χαριζόμενος θεράπευον
δήμῳ ἔνι Τρώων, ἀλλ’ ἄλλων ἦρχον ἑταίρων.
τὸν μὲν ἐγὼ κατιόντα βάλον χαλκήρεϊ δουρὶ
ἀγρόθεν, ἐγγὺς ὁδοῖο λοχησάμενος σὺν ἑταίρῳ·
νὺξ δὲ μάλα δνοφερὴ κάτεχ’ οὐρανόν, οὐδέ τις ἥμεας
ἀνθρώπων ἐνόησε, λάθον δέ ἑ θυμὸν ἀπούρας.
αὐτὰρ ἐπεὶ δὴ τόν γε κατέκτανον ὀξέϊ χαλκῷ,
αὐτίκ’ ἐγὼν ἐπὶ νῆα κιὼν Φοίνικας ἀγαυοὺς
ἐλλισάμην καί σφιν μενοεικέα ληΐδα δῶκα·

This is the first ‘lie’ Odysseus tells upon his arrival on Ithaca. He does not know that he is speaking to Athena and a scholiast explains his choices as if he were speaking to a suitor or one who would inform them.

Scholia V ad. Od. 13.267

“He explains that he killed Idomeneus’ son so that the suitors will accept him as an enemy of dear Odysseus. He says that he has sons in Crete because he will have someone who will avenge him. He says that the death of Orsilochus was for booty, because he is showing that he would not yield to this guy bloodlessly. He says that he trusted Phoenicians so that he may not do him wrong, once he has reckoned that they are the most greedy for profit and they spared him.”

τὸν μὲν ἐγὼ κατιόντα] σκήπτεται τὸν ᾿Ιδομενέως υἱὸν ἀνῃρηκέναι, ἵνα αὐτὸν πρόσωνται οἱ μνηστῆρες ὡς ἐχθρὸν τοῦ ᾿Οδυσσέως φίλου. ἑαυτῷ δὲ ἐν Κρήτῃ υἱούς φησιν εἶναι, ὅτι τοὺς τιμωρήσοντας ἕξει. καὶ τὸν ᾿Ορσιλόχου δὲ θάνατον λέγει διὰ τὴν λείαν, δεικνὺς ὅτι οὐδὲ ἐκείνῳ παραχωρήσει ἀναιμωτί. Φοίνιξι δὲ πιστεῦσαι λέγει, ἵνα μὴ ἀδικήσῃ, λογισάμενος ὅτι οἱ φιλοκερδέσταται αὐτοῦ ἐφείσαντο.
V.

Give me the loot.