Don't buy friends. Seneca, Epistles 2.19.10-12

Seneca does not think you can buy friends with favors. But you can get enemies this way.

Poteram tecum hac Maecenatis sententia parem facere rationem, sed movebis mihi controversiam, si novi te, nec voles quod debeo in aspero et inprobo accipere. Ut se res habet, ab Epicuro versura facienda est. Ante inquit circumspiciendum est cum quibus edas et bibas quam quid edas et bibas; nam sine amico visceratio leonis ac lupi vita est. Hoc non continget tibi nisi secesseris: alioquin habebis convivas quos ex turba salutantium nomenclator digesserit; errat autem qui amicum in atrio quaerit, in convivio probat. Nullum habet maius malum occupatus homo et bonis suis obsessus quam quod amicos sibi putat quibus ipse non est, quod beneficia sua efficacia iudicat ad conciliandos animos, cum quidam quo plus debent magis oderint: leve aes alienum debitorem facit, grave inimicum. Quid ergo? beneficia non parant amicitias? Parant, si accepturos licuit eligere, si collocata, non sparsa sunt. Itaque dum incipis esse mentis tuae, interim hoc consilio sapientium utere, ut magis ad rem existimes pertinere quis quam quid acceperit. Vale.

It was in my power to square accounts with you by offering nothing more than this observation of Maecenas, but if I know you, this will stir trouble, as you are not eager to accept payment of my debt in currency so chipped and debased. As matters stand, then, I am obliged to take another loan from Epicurus. Quoth he: "When it comes to dinner parties, you must consider the company before giving any thought to food or drink. Eating without a friend present is just the life of a lonely lion, or wolf." This saying will not reach you until you have spent some time alone. Otherwise, you will always have dinner-guests whom your dutiful servant sets apart from the crowd in your halls, just for you. But it is a mistake to look for a friend in the hall, and then prove his friendship at table. The man thoroughly occupied and obsessed with his own possessions owns nothing worse than the illusion that he has made friends by spreading his property around, using it to win hearts and minds. He forgets that some folk will inevitably repay greater debt with greater hatred. A little loan makes one of these haters your debtor; a large one turns him into your enemy. "What then? Don't friendships arise from mutual favors?" They do, but only if those favors are voluntary—placed carefully, to be taken or left, rather than scattered at random where none dare refuse. And so, as you begin the process of knowing your own mind in these matters, make good use meanwhile of this counsel from the wise: that you should judge the person who accepts a favor to be more significant than the favor itself. Farewell.