How to find the right Dhamma teacher

I tried to follow everything from the nissayamuccaka-course which I described in this answer, when I was still in a monk-hood by myself; and I had a low-quality teacher for about five years; before I found a perfect teacher from pa-auk forest monastery (this monastery also published other English-language Dharma articles here) who have all of the qualities listed below, that were specified in the tipitaka and commentary.
I met the pa-auk teacher too late, so I am being a layman now. However, it was my previous effort and experience which gave me the confidence to choose pa-auk to be my kammaṭṭhāna teacher.
The qualities of a teacher, and the operating procedure to choose and to apply with the teacher, have been briefly described in Chapter 4 of the Path of Purification.
Furthermore, in my opinion, the significant quality of a teacher is paṭisambhidā: because all ariya must have paṭisambhidā, at least in his kammaṭṭhāna. So he should have these qualities:

1. His teacher descent, he must derived from a tipitaka memorizer (buddha-sāvaka, suta-buddha; V.N. Mahāvagga Nissayamuccnakathā).
2. His enlightenment, he must achieved at least upacāra-samādhi and balava-vipassanā (4 paṭisambhidā; V.N. Mahāvagga Nissayamuccnakathā).
3. His tipitaka memory, he must graduated through at least nissayamuccaka-course (V.N. Pācittiyakaṇḍa Ovādakasikkhāpada's commentary).
4. His tipitaka understanding, he must not cut tipitaka off or make tipitaka conflict each other. Because tipitaka was memorized by single commentary teacher group at 1st saṅgāyanā, so it must be a single package that compatibility with each other (pro in tipitaka relation, dhamma-paṭisambhida&attha-paṭisambhidā).
5. His pali skill, he must understand pali in advance (nirutti-paṭisambhidā).
6. He must be a genius one (paṭibhāna-paṭisambhidā).

Furthermore, in tipitaka and commentary tradition, since mahākhandhaka of vinaya mahāvagga is completed authored by upāli in 1st saṇgāyanā, all layman's teachers must have all of these qualities, that concluded by upāli in bhikkhunovādakasikkhāpada's commentary (which I translate below as follows):

Qualities of nissayamuccaka-bhikkhu (teaching lay people)

1. Proficient to recite pāṭimokkha-pāli and to understand it's commentary.
2. Proficient to recite and to understand 4 bhāṇavāra (~1,000 syllable) of sutta and their commentary, to teach laymen on uposatha day.
3. Proficient to recite and to understand sutta for bhikkhu's life such as andhakavindasutta, mahālahulovādasutta, ambaṭṭhasutta, etc.
4. Proficient to recite and to understand sutta for teaching in 3 chances: banquet for saṅgha by layman (nidhikaṇdasutta), funeral ceremony (tirokuṭṭasutta), and auspicious ceremony (maṅgalasutta).
5. Enough understand to judge/to decide about saṇgha's ceremony such as uposatha, pavāraṇā, etc.
6. Proficient to recite and to understand his kammaṭṭhānā throughout the nibbāna-course.
7. 5 years experience in monk hood as a monk.

Qualities of bhikkuparisūpaṭṭhāpaka-bhikkhu (teaching bikkhus)
If above layman's teachers want to teach bhikkhus (ūpajjhā-ācāriya, nissaya-ācāriya), they must increase their skill level to all of the following qualities.
These are for abhivinaya teaching:

1. Proficient to recite mahāvibhagha and bhikkhunivibhaṅga (first 3 books of thai 45 books pali-tipitaka) of vinaya-pitaka-pali. At least, he can relay with the other 3 bhikkhu. Proficient to understand it's commentary, too.
2. Proficient to recite all saṇgha's ceremony in vinaya-pitaka mahāvagga and julavagga.
3. Proficient to recite 14 vatta in vattakhandhaka.

These are for abhidhamma (kammaṭṭhāna) teaching:

4. Proficient to recite one of this suttanta-pali: mūlapaṇṇassa (1st/3 parts of M.N.) for student in M.N. faculty, mahāvagga (2nd/3 parts of D.N.) for student in D.N. faculty, sagāthavagga+nidānavagga+khandhavāravagga of S.N. or mahāvagga of S.N. for student in S.N. faculty, before half of A.N. or after half of A.N. or ekakanipāta+dukanipāta of A.N. for student in A.N. faculty, jātaka+commentary (because kammaṭṭhāna was described in commentary) for student in jātaka faculty.

Qualities of bhikkunovdaka-bhikkhu (teaching bhikkunīs)
If above layman's teachers want to teach bhikkhunī, they must increase their skill level to all of these qualities:

1. Proficient to recite whole tipitaka-pali and commentary-pali. Or at least, he still must recite whole tipitaka, but he can recite just one commentary of suttanta, first 4 parts of commentary of 7 parts of abhidhamma. However, vinaya-commentary is what he must recite it all.

Reference: tipitaka and commentary of vinaya pācittiyakaṇḍa bhikkhunovādakasikkhāpada and vinaya mahāvagga mahākhandhaka.

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(I still find it difficult to reference the tipitaka and commentary using english resources: there's no translation, very long pages, confused categories, cutting some parts off the tipitaka, cutting commentary off from pali canon, etc.)

Related topic: https://buddhism.stackexchange.com/questions/3163/should-lay-buddhists-teach-the-dhamma