I have now twice shipped personal items of furniture into Thailand.

The first time I shipped from Hong Kong and ended up paying tea money of about 4500 baht.

This time round, from the UK, The company in Thailand is asking me for 70,000 baht all up. This does include some of the costs I paid direct in HK the previous time, but also includes 23,000 baht "Under the table' money and 11,000 baht to deliver and unpack at my house

I have tried transferring the consignment to the company I used 2 years ago and now they want an extortionate amount too?

The make up of the goods is very similar.

Anyone know of a decent shipping agent who won't rip me off?

I took delivery last week of a shipment (17 cu metres in a container to myself) of personal items from Paris to Chiang Rai.

The all-in door to door cost was 220 000 baht. The customs tea money wanted/given was 24 000 baht.

I don't know how reasonable these costs are. (I provide them in case they give you (or anyone else) a tool for comparison.) The service was fine. The company was AGS Four Winds.

In general imports of personal items into Thailand are subject to import duty, and is levied according to the type of goods and the declared value. If the goods are already in Thailand and customs paperwork has been submitted then it's unlikely that assigning a new local agent will help much at all.

Your previous shipment might have been sent before personal goods were subject to import duty.