DevExpress Lookupedit Set Selected Value

Question

I have following Grid where it populates InquiryDetails in the Win Form Load event

private void frmInquiryManagement_Load(object sender, EventArgs e)
        {

            InquiryService inquiry = new InquiryService();
            clearGetInquiry();

            DataTable dt = InfoPCMS.db.executeSelectQuery("select * from Inquiry");
            gridInquiryList.DataSource = dt;

            DataTable dt2 = InfoPCMS.db.executeSelectQuery("select * from Customer");
            txtCustomer.Properties.DataSource = dt2;
            txtCustomer.Properties.ValueMember = "Id";
            txtCustomer.Properties.DisplayMember = "CustomerName";
            txtCustomer.Properties.NullText = "Please Select Customer";

            txtCustomer.Properties.Columns.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("CustomerName"));
            txtCustomer.Properties.Columns.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("Address"));
            txtCustomer.Properties.ShowHeader = false;

            int nextid = inquiry.getNextId();
            txtInquiryNo.Text = nextid.ToString();
        }

By double clicking on a row, it searches for all the details and displays in "Get Inquiries" Tab as follows, code of that is below the image

private void selectInquiry(object sender, EventArgs e)
        {


            btnAddInquiry.Enabled = false;
            btnUpdate.Enabled = true;
            txtInquiryNo.Enabled = false;


            String inquiryno = gridView1.GetFocusedDataRow()["InquiryNumber"].ToString();

            InquiryService inquiry = new InquiryService();
            inquiry = inquiry.searchInquiry(inquiryno);
            if (inquiry != null)
            {

                txtInquiryNo.Text = inquiry.InquiryNumber.ToString();
                //txtDate.Text = inquiry.InquiryDate;
                txtDate.Text = InfoPCMS.conversion.convertDate(inquiry.InquiryDate);

                txtCustomer.EditValue = inquiry.CustomerID.ToString();
                txtInquiryTaken.Text = inquiry.InquiryTaken;
                txtInspectionDetails.Text = inquiry.InspectionDetails;
                txtProblemNature.Text = inquiry.ProblemNature;
                txtProblemSource.Text = inquiry.ProblemSource;
                txtSiteResponsible.Text = inquiry.SiteResponsible;
                txtQuotationNo.Text = inquiry.QuotationNumber.ToString();
                txtFollowupDetails.Text = inquiry.FollowupDetails;
                txtInspectionDone.Text = inquiry.InspectionDone;

                tabInquiryManagement.SelectedTabPage = xtraTabPage2;

            }
            else
            {

                MessageBox.Show(InfoPCMS.message.GET_NO_SUCH_RECORD_INFORMATION(), "Information");

            }
        }

First time you search it works fine, But after when you clear all the fields and the page and try another record it will give all the records but the Lookupedit value to its null state as follows,

private void clearGetInquiry() {

            txtInquiryNo.Text = "";
            txtDate.Text = "";
            txtCustomer.EditValue = null;

            txtInquiryTaken.Text = "";
            txtInspectionDetails.Text = "";
            txtProblemNature.Text = "";
            txtProblemSource.Text = "";
            txtSiteResponsible.Text = "";
            txtQuotationNo.Text = "";
            txtFollowupDetails.Text = "";
            txtInspectionDone.Text = "";

            btnAddInquiry.Text = "Add Inquiry";

            InquiryService inquiry = new InquiryService();
            int nextid = inquiry.getNextId();
            txtInquiryNo.Text = nextid.ToString();

            tabInquiryManagement.SelectedTabPage = xtraTabPage1;

            btnAddInquiry.Enabled = true;
            btnUpdate.Enabled = false;
            txtInquiryNo.Enabled = true;

        }

How can I get rid of this issue? (This happens even when you do the search after going into the "Get Inquiries" Tab and come.