Karan, it is a very valid question and not easy to answer. Personally, this prevented me for the first 7 years in India to accept any of the many spiritual personalities I met as “my guru”. i stuck to gurus who had left their bodies, like Ramana Maharshi.
I feel the main thing is a sincere aspiration. After 7 years I considered Satya Sai Baba as my guru, more or less convinced myself into it that he possibly cannot tell a lie when he claims to be an avatar. I developed full faith in him and it was helpful. Yet after 7 years again, I somehow lost faith in him from one moment to the other. It was time to move on.
Ultimately it is the Ishta deva within (atman) who is the guru, but to consider this presence as really real is not so easy and a physical guru as a projection helps.
On the other hand, nowadays we can get the knowledge via books that were not available earlier. Then a guru was a must.
Probably the solution is to trust the divine inner guidance and be sensitive to what you feel about some guru, without being too much influenced by his other disciples. Ultimately, whatever is meant to happen, will happen. You can’t go really wrong as long as your motivation and aspiration are pure.

yadā yadā hi dharmasya, glānir bhavati bhārata.
abhyutthānam adharmasy, tadatmanam srijamyaham.
paritrānāya sādhūnām, vināśāya ca dushkritām.
dharma-sansthāpanārthāya, sambhavāmi yuge yuge
Translation:
Whenever and wherever there is a decline in religious practice (of Sanatana Dharma), O descendant of Bharata, and a predominant rise of irreligion – at that time I descend Myself.
To deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion (Sanatana Dharma), I Myself appear, millennium after millennium.

(here dharma has been translated as religious practice though dharma is much more than the literal meaning of word religion in English. Since there’s no equivalent of Dharma in English we’ve chosen this.)

@Kumar,
Nope westerners are not into Bhakti yoga, and if at all most westerners are more into Jnana Yoga with their insatiable appetite for hindu philosophy which is vast and complex. They are very knowledgeable in the scriptures. There are a few all white hindu monasteries that spread the gospel of shaivism with all potential ambiguity removed from the sampradaya. Also this monastery is very inclusive and keep saying good things about all other hindu sampradayas out there. Check it out on Himalayan Academy out of Hawaii. Cheers.

The four ancient aims of Hindu life are Dharma (integrity), Artha (prosperity), Kama (pleasure), and Moksha (enlightenment). All are necessary for happiness, but individuals will tend to give more emphasis to an aim or aims that suit their upbringing, propensity or innate urge.Regards.