I do not think so. A bank letter of guarantee, would seem to be a letter from your bank stating that you have sufficient funds to purchase an object or objects not totaling more than $xxx.xx in price. A letter of credit, is simply a line of credit your bank may extend to you. It usually has a very short payback period and interest is charged. It is basically a short term loan that you can use as needed. Some banks will issue a special checkbook for the letter of credit, or you can deposit it in your account. However, because bad checks are written all the time, I could see an auction house asking for a letter of guarantee that certifies you have the funds you are seeking to spend.