Unfortuneately there is little interest in Trix twin these days as it will not run on anything other than Trix twin track and there are only about 200 collectors of Trix twin worldwide and they already have complete collections.
Only mint and boxed stuff has any hope of selling as collectors do want to improve on existing items held.
I am surprised by the high valuation you were given as I can buy shedloads of the stuff for £100 to £200 but it takes up so much storage space I don't bother and I cannot sell the stuff on.
For those who want an incredibly cheap and massive start up with loads of track and trains and who are not bothered about apearance then I would recomend picking up an old Trix twin collection as you will get a massive amount for your money. You won't be able to run anything else though but Trix twin. Ideal for the kids perhaps?
Sorry if I appear so blunt but if you value the trains (if they work) at about £10 each average, the wagons and coaches at about £2 each average and the track at about 5p per item and 25p for points then that would be a good guide.
Did the professionals valuing the collection make you an offer?
Its one thing to value a collection but another thing entirely to part with hard cash!
Happy modelling
Gary