Do You Trust In Stanley Gibbons ???

My friend talked to me a little while ago, he went to another dealer stamps and Display 9000 pounds in the event of selling directly without going to auction.
  What do you advise me?

Stanley Gibbons have many many years of experience when it comes to stamp evaluation. I'd advise taking the Stanley Gibbons offer as that would possibly reflect the true value of your stamps. Going to yet another dealer in stamps would just bump up the 9000 pounds offer once again and you'd have to go to yet another one just in case and thus never reach an end to offers.

Do I sell or wait?
  I have until next Monday to decide, because my friend will return to Jordan.
I hope that you recommend and without seriously to taunt.

Same, only you can make that decision. I have no advise for you on whether to sell or not.
I will answer your original question in that I believe Stanley Gibbons is a trustworthy business man.

Good luck. I hope everything works out for the best.

Is the second dealer offering to buy your stamps for £9000? If they are why take SG's £1700?

Terry

Same a little more information as to how you obtained your stamps and from what source(s)? Did you buy these stamps one at a time or in small collections or a few big collections?

Trust no one, verify and be your own advocate.
Double check, cross check and check again.

Let's face it, there's a premium to be paid when you want to do something quickly.
Just like the collecting side of it. If you have unlimited funds you can put together a stunning collection much quicker then if you have a small budget. Then it can take many years to put together a collection.

When selling a collection if you're willing to do the work yourself and take your time, you will most likely make more profit. If you want to "unload" a collection quickly it's likely you will not make as much profit.

Timm says, verify and be your own advocate.
Double check, cross check and check again.

That's good advice....., that takes time and effort.

Nobody has pointed this out, but selling to a dealer will get you less than 50% of what selling to a collector will bring because they have to make a profit selling the collection to someone else. They bear all the risk and have to spend all of the time to resell the collection. I'm not sure why anyone in their right mind doesn't understand that, but apparently, and this isn't just in stamps, people think that they deserve to be paid retail rates when selling to resellers.