Some truth to that liner that "no one can investigate like a scorned wife". Some women are not only very motivated, but they also have their very sharp instincts and info intelligence to guide them to evidence.
But there is also another group of women who can only weep and cry helplessly when faced with any stage of adultery.
Then you have the another group who cannot stop themselves from marching up to slap the "vixen" before even gathering any proof that can hold water in court.
And then you have the other few who would announce to the husband and the world that she has got a "PI" on his tracks even before she has one.
And the list goes on.
On the other interesting point raised, some may ask, is it also easier to be spotted if its the wife tailing the dude instead of complete strangers? Probably. Not that its impossible though, just gotta take note of details and needs good planning and help.
About 7 years back, a few of us played "PI" before for a friend. To agree to her requests to undertake this role, we knew we were putting the friendship with the husband on the line, just that the circumstances were such that we had to help her.
So, the few of us, in two teams, began our stakeout in inconspicuous cars we had to swop with other friends from other social circles, armed with fully charged long range walkie-talkies, repellent, fans, water, cameras, VRs, maps, etc., and yummy fried chicken wings, which we can testify now it is not the best "PI" snack, yummy as they were but leaves the fingers very oily and sticky.
Now that we are significantly older, we understand more of and how to extract and optimise the value of engaging professional services where possible.
In short, it is a vying measure between accurate intelligence and persistance. So means to say, if you are one who is able to grasp accurate info and pass the accurate info to your PI, you should have a scoop nearly immediately thus not incurring unnecessary costs. Similar too if you engage friends' help.
I think, many a times, costs go up because there are alot of misses and empty leads. So, gotta factor this point in when negotiating with the PIs shortlisted so that you put a lid on your costs.