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I'm afraid that there's no one-sized-fits-all answer to that question. I'd be very wary of being charged by the link, because anyone who focuses on quantity is going to inevitably sacrifice quality. If I promise to build you 50 links for $500, you'll get what you paid for (i.e. not much). Worse yet, below a certain quality threshold, you're taking a long-term risk. In other words, you won't just risk spending your money poorly - you'll risk a penalty or serious SEO problems. On the other hand, I definitely don't think you should settle for "give us some money and we will do our best" - your link-building company should definitely have a plan and be transparent about it. Preferably, that's going to be a mix of helping you develop content and build/attract links to it, but it should be quantifiable. Anything related to real estate is going to be competitive, and that means expensive (done right). I'd definitely stay local, honestly - someone who knows the UK and even London market will have not only more relevant experience but more relevant connections. A bunch of links from Istanbul aren't going to help you much. A really great firm may even have PR connections, but obviously that's a different price level.