Here is the safe transaction methodology when large sums are involved.:
1- Ask for pay order. These can not be blocked that easily. Make sure to confirm that pay order is not bogus. Take buyer with you to bank to confirm its authenticity.
2- Ask for cash but do not take it. Ask buyer to come with you to your bank and deposit cash in you account. Handover the documents to buyer inside bank to assure him you are also not doing any fraud.
Never ever, I repeat never ever do transactions on check. Checks have highest rate of fraud involved.