Strange customs

They sure had some strange customs back in the day.  Check this out.

Acts 21:17-26(NKJV)

And when we had come to Jerusalem, the brethren received us gladly. 

On the following day Paul went in with us to James, and all the elders were present. 

When he had greeted them, he told in detail those things which God had done among the Gentiles through his ministry. 

And when they heard it, they glorified the Lord. And they said to him, “You see, brother, how many myriads of Jews there are who have believed, and they are all zealous for the law; 

but they have been informed about you that you teach all the Jews who are among the Gentiles to forsake Moses, saying that they ought not to circumcise their children nor to walk according to the customs. 

What then? The assembly must certainly meet, for they will hear that you have come. 

Therefore do what we tell you: We have four men who have taken a vow. 

Take them and be purified with them, and pay their expenses so that they may shave their heads, and that all may know that those things of which they were informed concerning you are nothing, but that you yourself also walk orderly and keep the law. 

But concerning the Gentiles who believe, we have written and decided that they should observe no such thing, except that they should keep themselves from things offered to idols, from blood, from things strangled, and from sexual immorality.”

Then Paul took the men, and the next day, having been purified with them, entered the temple to announce the expiration of the days of purification, at which time an offering should be made for each one of them.

How does that prove that Paul is telling the truth?  Doesn't it seem more like he would be buying their testimony with this approach?