In addition to making a guaranty, the guarantor may enter into a service contract at the time of the sale or at any other time with the person guaranteed. In addition to entering into a service contract, the provider may make a guaranty at the time of the sale or at any other time to the person guaranteed. The guarantor or provider may designate a representative to perform the duties under this subtitle. However, this designation does not relieve the guarantor or provider of the duties to the person guaranteed.