There are some exceptions, but they are rare, they have access to funds, and they typically built their empire when the timing was right and got lucky.Likewise, it's not often that you can buy a house and sell it for big money six months later.

I am attempting to sign up but not sure if I will get access in time.

Hi,I wanted to ask if there is a lock box (to put keys inside) that I can buy that doesn't require WIFI at the lock box location. However, I want to be able to change the lock box code or make it so that I can lock it...

Called a locksmith and gained access.

And they have a huge amount of beaches much nicer than Tulum's or Colombia's, which are much more easily accessible from pretty much anywhere in the world where most tourism originates.Yet, they won't do it.

This is one of the reasons I would be very hesitant to allow an arbitrager access to my property.

Investors/lenders can have overlays that are more restrictive, but generally can't waive this.

Is this market accessible for the average investor in the UK, or is it exclusively banks and hedge funds who buy/sell these sorts of instruments?

Some areas have conservation easements , you may cut a deal with the local government where if you put a restriction on the property to let it go natural they may pay you . 

There are different philosophies to real estate investing and it depends on your finances, if you have less capital, you're going to have to be more creative on deals and need cash flow, if you have access to some capital, you can tolerate cash flow losses.