Tell them all the new purchases are second hand and are worth more than they cost! (And are therefore an investment)
Never have a joint account. (And if you do, buy the guns with cash)
Always knock 1/3rd to 1/2 off the actual price.
Don't keep reciepts.
Tell them it's not yours, your just setting it up for your mate!!
And my favourite one, As a gardener and handyman I provide pest control services and told her the guns where bought by the business and help to offset my tax bill, therefore saving me money!!