School that I won’t go to paid too much money for my trip to the Visitiation weekend

[Newstar2020]

I got accepted to the chemistry programs of two schools. I almost decide to go to school A.  
However, I still want to go to visit school B because they accepted me and I am curious how it feels like to study there and I also want to meet new people and learn something new too. They just paid $500 for my flight ticket (I’m an international student who doesn’t have a car) and they will also cover all the cost while during my visit. I know I am not doing anything wrong, but I kinda feel bad. I actually had been hesitant in confirming with them about my visit because I know I won’t go to this school. There is a small chance that I may end up choosing this school because I got a lot of advice that I shouldn’t choose my school before the visits but it won’t apply to my case because I see a big gap between the two schools. 
So my questions are: will they be frustrated when I decline their offer after the visit? Is it common that the school will pay that much for your visit? Any suggestion on how to craft the email to politely inform them of my decision?

*I apologize in advance if my English causes any confusion 

[Modulus]

Schools that offer money for you to travel for a visit are interested in recruiting you. If there was absolutely no chance you would go then maybe you would want to turn down the offer to visit, but if you can give them a chance to impress you and you have the time and ability to visit, I think you should do so!  You should not feel guilty about spending their money.  They will understand if you choose a different opportunity in the end.

[Charlie19]

I think it's OK to have visits paid by schools that you have little chance to attend. You paid for the application fee, they want you to have a visit, it's fair. No worry about the cost, I think they probably use others' application fee to cover all the expenses during your visit.

[Gatech_ST]

I would personally go there with an open, see the place, talk to people and just gauge how fit you are there. There is more to school then ranking!

[Crucial BBQ]

The point of visitations are to sell the program to you.  They know that not everyone who gets invited will attend.  

This is not directed at you Newstar2020, but to those who would visit schools/programs they know they are not going to attend, well, that says something about their character.