Sometimes mechanics will write the date they changed the belt on the cover. Other times you have to look for tool marks on the timing belt cover and/or cranksha

Sometimes mechanics will write the date they changed the belt on the cover. Other times you have to look for tool marks on the timing belt cover and/or crankshaft pulley. But the best way is to have paperwork showing it's been done. If none of the above are definitive, go ahead and pay to have it done - it'll be far cheaper than if the belt breaks.