Hi,

You can add workflow to res.partner model. Inorder to have only approved customers in quotations, opportunity etc, later you can domain filter the many2one field using state = approved.

For eg, am adding just two states "New" and "Approved". Please try the following code:

in your python file:

class res_partner(models.Model):
    
    _inherit = 'res.partner'
    
    STATE_SELECTION = [
        ('new', 'New'),
        ('approved', 'Approved'),
        
    ]
    state = fields.Selection(STATE_SELECTION, 'Status', readonly=True,
                                  help="New customer created. "
                                       "New Customer approved. ",
                                  select=True,default='new')
    @api.multi
    def write(self, vals):
        
        if self.state == 'approved':
            vals.update({'state':'new'})
       
        return super(res_partner, self).write(vals)
    
    @api.multi
    def approve_customer(self):
        self.write({'state':'approved'})
    

in your workflow xml file:

<?xml version="1.0" encoding="utf-8"?><openerp>
    <data>

        <record id="customer_flow" model="workflow">
            <field name="name">Custmer Workflow</field>
            <field name="osv">res.partner</field>
            <field name="on_create">True</field>
        </record>

        <record id="act_new" model="workflow.activity">
            <field name="wkf_id" ref="customer_flow"/>
            <field name="flow_start">True</field>
            <field name="name">new</field>
        </record>
        <record id="act_approved" model="workflow.activity">
            <field name="wkf_id" ref="customer_flow"/>
            <field name="name">approved</field>
          	<field name="flow_stop">True</field>
        </record>
        <record id="trans_new_confirmed" model="workflow.transition">
            <field name="act_from" ref="act_new"/>
            <field name="act_to" ref="act_approved"/>
            <field name="signal">customer_confirm</field>
        </record>
        
         
    </data>
</openerp>

in your xml view file:

	<record id="view_partner_form_with_states" model="ir.ui.view">
	    <field name="name">Add states to customer</field>
	    <field name="model">res.partner</field>
	    <field name="inherit_id" ref="base.view_partner_form"/>
	    <field name="arch" type="xml">
	        
	            <sheet position="before">
	                <header>
	                    <button name="approve_customer" states="new" type="object" string="Approve" class="oe_highlight" />
	                    <field name="state" widget="statusbar" statusbar_visible="new,approved" statusbar_colors='{"new":"blue","approved":"blue"}' readonly="1" />
	                </header>
	            </sheet>
		  </field>
	</record>

Hope this helps!