@Linkat,
First of all find out the scrap value, you should be able to workout the carat of the diamonds from the size, and with it to see how heavy it is, at least 50% of that will be gold and prices are available online.
That gives you a base line, after that try and find something about the watch, it may only be worth scrap value, but it could be worth significantly more depending on make, age, condition etc.
In the last episode of Only Fools and Horses Del Boy makes his fortunes from some old watch that once belonged to a famous watchmaker.
Those places that advertise on the telly will only give scrap value, and you’d be better off going somewhere local with a fixed address.
And shop around, not everywhere gives the same price.
Those places should be a last resort, if you can sell the watch to someone who wants it because of what it is, you’ll get a better price.