Thank you for the question. Firstly, this is something your conveyancing solicitor will take care of for you as a matte of course. However, for peace of mind. It will depend on when you purchase the property C and sell the property B. However if the situation arrises where you appear to have "double paid" or over paid on the LBTT, you have 18 months to obtain a refund on this tax. So, if you purchase a property and LBTT is triggered due to the fact you own a secondary property, this tax can be refunded once the "triggering" property is disposed of, so long as this is done within the 18 month period. I would advise using one solicitor to deal with all sales and purchases and express your concerns to them about this matter, however as stated initially, they should know this and deal with it as a matter of course.
I shall provide you with a helpful link that will assist you in finding a solicitor/representative near your local area. This will provide you with someone nearby your area who can assist you if required.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
https://solicitors.lawsociety.org.uk/ (England)
https://www.lawscot.org.uk/find-a-solicitor/ (Scotland)
https://www.lawsociety.ie/Find-a-Solicitor/Solicitor-Firm-Search/ (Ireland)
https://www.lawsoc-ni.org/solicitors (N. Ireland)
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