How to handle a stranger's request to come aboard for a look.

[FlyTheCoop]

We were in a bay with a number of other boats when along came a very nice couple in a tender saying they were thinking of buying a catamaran and was it possible to come on board for a look. No introductions or other other small talk. I politely refused and said we were having lunch right now but they were welcome to check back later.

On one hand it's a nice complement, on the other, an invasion of privacy.

Just interested in how other cruisers have handled the same request.